[add] i18n support zh,en

api/app/i18n/README.md

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+# Internationalization (i18n) Module
+
+This module provides internationalization support for the MemoryBear API.
+
+## Components
+
+- `service.py` - Translation service and core translation logic
+- `middleware.py` - Language detection middleware
+- `dependencies.py` - FastAPI dependency injection functions
+- `exceptions.py` - Internationalized exception classes
+
+## Usage
+
+### Basic Translation
+
+```python
+from app.i18n import t
+
+# Simple translation
+message = t("common.success.created")
+
+# Parameterized translation
+message = t("common.validation.required", field="Name")
+```
+
+### Enum Translation
+
+```python
+from app.i18n import t_enum
+
+# Translate enum value
+role_display = t_enum("workspace_role", "manager")
+```
+
+### In FastAPI Endpoints
+
+```python
+from fastapi import Depends
+from app.i18n.dependencies import get_translator
+
+@router.post("/workspaces")
+async def create_workspace(
+    data: WorkspaceCreate,
+    t: Callable = Depends(get_translator)
+):
+    workspace = await workspace_service.create(data)
+    return {
+        "success": True,
+        "message": t("workspace.created_successfully"),
+        "data": workspace
+    }
+```
+
+## Configuration
+
+See `app/core/config.py` for i18n configuration options:
+
+- `I18N_DEFAULT_LANGUAGE` - Default language (default: "zh")
+- `I18N_SUPPORTED_LANGUAGES` - Supported languages (default: "zh,en")
+- `I18N_ENABLE_TRANSLATION_CACHE` - Enable caching (default: true)
+- `I18N_LOG_MISSING_TRANSLATIONS` - Log missing translations (default: true)

api/app/i18n/__init__.py

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+"""
+Internationalization (i18n) module for MemoryBear Enterprise.
+
+This module provides complete i18n support for the backend API including:
+- Translation loading from multiple directories (community + enterprise)
+- Translation service with caching and fallback
+- Language detection middleware
+- Dependency injection for FastAPI
+- Convenience functions for easy usage
+
+Usage:
+    from app.i18n import t, t_enum
+
+    # Simple translation
+    message = t("common.success.created")
+
+    # Parameterized translation
+    error = t("common.validation.required", field="名称")
+
+    # Enum translation
+    role_display = t_enum("workspace_role", "manager")
+"""
+
+from app.i18n.dependencies import (
+    get_current_language,
+    get_enum_translator,
+    get_translator,
+)
+from app.i18n.exceptions import (
+    BadRequestError,
+    ConflictError,
+    FileNotFoundError,
+    FileTooLargeError,
+    ForbiddenError,
+    I18nException,
+    InternalServerError,
+    InvalidCredentialsError,
+    InvalidFileTypeError,
+    NotFoundError,
+    QuotaExceededError,
+    RateLimitExceededError,
+    ServiceUnavailableError,
+    TenantNotFoundError,
+    TenantSuspendedError,
+    TokenExpiredError,
+    TokenInvalidError,
+    UnauthorizedError,
+    UserAlreadyExistsError,
+    UserNotFoundError,
+    ValidationError,
+    WorkspaceNotFoundError,
+    WorkspacePermissionDeniedError,
+    get_current_locale,
+    set_current_locale,
+)
+from app.i18n.loader import TranslationLoader
+from app.i18n.logger import (
+    TranslationLogger,
+    get_translation_logger,
+    log_missing_translation,
+    log_translation_error,
+)
+from app.i18n.middleware import LanguageMiddleware
+from app.i18n.service import (
+    TranslationService,
+    get_translation_service,
+    t,
+    t_enum,
+)
+
+__all__ = [
+    "TranslationLoader",
+    "LanguageMiddleware",
+    "TranslationService",
+    "get_translation_service",
+    "t",
+    "t_enum",
+    "get_current_language",
+    "get_translator",
+    "get_enum_translator",
+    # Context management
+    "get_current_locale",
+    "set_current_locale",
+    # Logging
+    "TranslationLogger",
+    "get_translation_logger",
+    "log_missing_translation",
+    "log_translation_error",
+    # Exception classes
+    "I18nException",
+    "BadRequestError",
+    "UnauthorizedError",
+    "ForbiddenError",
+    "NotFoundError",
+    "ConflictError",
+    "ValidationError",
+    "InternalServerError",
+    "ServiceUnavailableError",
+    "WorkspaceNotFoundError",
+    "WorkspacePermissionDeniedError",
+    "UserNotFoundError",
+    "UserAlreadyExistsError",
+    "TenantNotFoundError",
+    "TenantSuspendedError",
+    "InvalidCredentialsError",
+    "TokenExpiredError",
+    "TokenInvalidError",
+    "FileNotFoundError",
+    "FileTooLargeError",
+    "InvalidFileTypeError",
+    "RateLimitExceededError",
+    "QuotaExceededError",
+]

api/app/i18n/cache.py

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+"""
+Advanced caching system for i18n translations.
+
+This module provides:
+- LRU cache for hot translations
+- Lazy loading mechanism
+- Memory optimization
+- Cache statistics
+"""
+
+import logging
+from functools import lru_cache
+from typing import Any, Dict, Optional
+from collections import OrderedDict
+import time
+
+logger = logging.getLogger(__name__)
+
+
+class TranslationCache:
+    """
+    Advanced translation cache with LRU eviction and lazy loading.
+    
+    Features:
+    - LRU cache for frequently accessed translations
+    - Lazy loading to reduce startup time
+    - Memory-efficient storage
+    - Cache hit/miss statistics
+    """
+    
+    def __init__(self, max_lru_size: int = 1000, enable_lazy_load: bool = True):
+        """
+        Initialize the translation cache.
+        
+        Args:
+            max_lru_size: Maximum size of LRU cache for hot translations
+            enable_lazy_load: Enable lazy loading of locales
+        """
+        self.max_lru_size = max_lru_size
+        self.enable_lazy_load = enable_lazy_load
+        
+        # Main cache: {locale: {namespace: {key: value}}}
+        self._main_cache: Dict[str, Dict[str, Any]] = {}
+        
+        # LRU cache for hot translations
+        self._lru_cache: OrderedDict = OrderedDict()
+        
+        # Loaded locales tracker
+        self._loaded_locales: set = set()
+        
+        # Statistics
+        self._stats = {
+            "hits": 0,
+            "misses": 0,
+            "lru_hits": 0,
+            "lru_misses": 0,
+            "lazy_loads": 0
+        }
+        
+        logger.info(
+            f"TranslationCache initialized with LRU size: {max_lru_size}, "
+            f"lazy loading: {enable_lazy_load}"
+        )
+    
+    def set_locale_data(self, locale: str, data: Dict[str, Any]):
+        """
+        Set translation data for a locale.
+        
+        Args:
+            locale: Locale code
+            data: Translation data dictionary
+        """
+        self._main_cache[locale] = data
+        self._loaded_locales.add(locale)
+        logger.debug(f"Loaded locale '{locale}' into cache")
+    
+    def get_translation(
+        self,
+        locale: str,
+        namespace: str,
+        key_path: list
+    ) -> Optional[str]:
+        """
+        Get translation from cache with LRU optimization.
+        
+        Args:
+            locale: Locale code
+            namespace: Translation namespace
+            key_path: List of nested keys
+            
+        Returns:
+            Translation string or None if not found
+        """
+        # Build cache key for LRU
+        cache_key = f"{locale}:{namespace}:{'.'.join(key_path)}"
+        
+        # Check LRU cache first (hot translations)
+        if cache_key in self._lru_cache:
+            self._stats["lru_hits"] += 1
+            self._stats["hits"] += 1
+            # Move to end (most recently used)
+            self._lru_cache.move_to_end(cache_key)
+            return self._lru_cache[cache_key]
+        
+        self._stats["lru_misses"] += 1
+        
+        # Check main cache
+        if locale not in self._main_cache:
+            self._stats["misses"] += 1
+            return None
+        
+        if namespace not in self._main_cache[locale]:
+            self._stats["misses"] += 1
+            return None
+        
+        # Navigate through nested keys
+        current = self._main_cache[locale][namespace]
+        for key in key_path:
+            if isinstance(current, dict) and key in current:
+                current = current[key]
+            else:
+                self._stats["misses"] += 1
+                return None
+        
+        # Return only if it's a string value
+        if not isinstance(current, str):
+            self._stats["misses"] += 1
+            return None
+        
+        self._stats["hits"] += 1
+        
+        # Add to LRU cache
+        self._add_to_lru(cache_key, current)
+        
+        return current
+    
+    def _add_to_lru(self, key: str, value: str):
+        """
+        Add translation to LRU cache.
+        
+        Args:
+            key: Cache key
+            value: Translation value
+        """
+        # Remove oldest if cache is full
+        if len(self._lru_cache) >= self.max_lru_size:
+            self._lru_cache.popitem(last=False)
+        
+        self._lru_cache[key] = value
+    
+    def is_locale_loaded(self, locale: str) -> bool:
+        """
+        Check if a locale is loaded.
+        
+        Args:
+            locale: Locale code
+            
+        Returns:
+            True if locale is loaded
+        """
+        return locale in self._loaded_locales
+    
+    def get_loaded_locales(self) -> list:
+        """
+        Get list of loaded locales.
+        
+        Returns:
+            List of locale codes
+        """
+        return list(self._loaded_locales)
+    
+    def clear_lru(self):
+        """Clear the LRU cache."""
+        self._lru_cache.clear()
+        logger.info("LRU cache cleared")
+    
+    def clear_locale(self, locale: str):
+        """
+        Clear cache for a specific locale.
+        
+        Args:
+            locale: Locale code
+        """
+        if locale in self._main_cache:
+            del self._main_cache[locale]
+            self._loaded_locales.discard(locale)
+        
+        # Clear related LRU entries
+        keys_to_remove = [k for k in self._lru_cache if k.startswith(f"{locale}:")]
+        for key in keys_to_remove:
+            del self._lru_cache[key]
+        
+        logger.info(f"Cleared cache for locale '{locale}'")
+    
+    def clear_all(self):
+        """Clear all caches."""
+        self._main_cache.clear()
+        self._lru_cache.clear()
+        self._loaded_locales.clear()
+        logger.info("All caches cleared")
+    
+    def get_stats(self) -> Dict[str, Any]:
+        """
+        Get cache statistics.
+        
+        Returns:
+            Dictionary with cache statistics
+        """
+        total_requests = self._stats["hits"] + self._stats["misses"]
+        hit_rate = (
+            self._stats["hits"] / total_requests * 100
+            if total_requests > 0
+            else 0
+        )
+        
+        lru_total = self._stats["lru_hits"] + self._stats["lru_misses"]
+        lru_hit_rate = (
+            self._stats["lru_hits"] / lru_total * 100
+            if lru_total > 0
+            else 0
+        )
+        
+        return {
+            "total_requests": total_requests,
+            "hits": self._stats["hits"],
+            "misses": self._stats["misses"],
+            "hit_rate": round(hit_rate, 2),
+            "lru_hits": self._stats["lru_hits"],
+            "lru_misses": self._stats["lru_misses"],
+            "lru_hit_rate": round(lru_hit_rate, 2),
+            "lru_size": len(self._lru_cache),
+            "lru_max_size": self.max_lru_size,
+            "loaded_locales": len(self._loaded_locales),
+            "lazy_loads": self._stats["lazy_loads"]
+        }
+    
+    def reset_stats(self):
+        """Reset cache statistics."""
+        self._stats = {
+            "hits": 0,
+            "misses": 0,
+            "lru_hits": 0,
+            "lru_misses": 0,
+            "lazy_loads": 0
+        }
+        logger.info("Cache statistics reset")
+    
+    def get_memory_usage(self) -> Dict[str, Any]:
+        """
+        Estimate memory usage of the cache.
+        
+        Returns:
+            Dictionary with memory usage information
+        """
+        import sys
+        
+        main_cache_size = sys.getsizeof(self._main_cache)
+        lru_cache_size = sys.getsizeof(self._lru_cache)
+        
+        # Rough estimate of nested data
+        for locale_data in self._main_cache.values():
+            main_cache_size += sys.getsizeof(locale_data)
+            for namespace_data in locale_data.values():
+                main_cache_size += sys.getsizeof(namespace_data)
+        
+        return {
+            "main_cache_bytes": main_cache_size,
+            "lru_cache_bytes": lru_cache_size,
+            "total_bytes": main_cache_size + lru_cache_size,
+            "main_cache_mb": round(main_cache_size / 1024 / 1024, 2),
+            "lru_cache_mb": round(lru_cache_size / 1024 / 1024, 2),
+            "total_mb": round((main_cache_size + lru_cache_size) / 1024 / 1024, 2)
+        }
+
+
+@lru_cache(maxsize=128)
+def get_cached_translation_key(locale: str, namespace: str, key: str) -> str:
+    """
+    LRU cached function for building translation cache keys.
+    
+    This reduces string concatenation overhead for frequently accessed keys.
+    
+    Args:
+        locale: Locale code
+        namespace: Translation namespace
+        key: Translation key
+        
+    Returns:
+        Cache key string
+    """
+    return f"{locale}:{namespace}:{key}"

api/app/i18n/dependencies.py

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+"""
+FastAPI dependency injection functions for i18n.
+
+This module provides dependency injection functions that can be used
+in FastAPI route handlers to access the current language and translator.
+"""
+
+import logging
+from typing import Callable
+
+from fastapi import Request
+
+from app.i18n.service import get_translation_service
+
+logger = logging.getLogger(__name__)
+
+
+async def get_current_language(request: Request) -> str:
+    """
+    Get the current language from the request context.
+
+    This dependency extracts the language that was determined by the
+    LanguageMiddleware and stored in request.state.
+
+    Args:
+        request: FastAPI request object
+
+    Returns:
+        Language code (e.g., "zh", "en")
+
+    Usage:
+        @router.get("/example")
+        async def example(language: str = Depends(get_current_language)):
+            return {"language": language}
+    """
+    # Get language from request state (set by LanguageMiddleware)
+    language = getattr(request.state, "language", None)
+
+    if language is None:
+        # Fallback to default language if not set
+        from app.core.config import settings
+        language = settings.I18N_DEFAULT_LANGUAGE
+        logger.warning(
+            "Language not found in request.state, using default: "
+            f"{language}"
+        )
+
+    return language
+
+
+async def get_translator(request: Request) -> Callable:
+    """
+    Get a translator function bound to the current request's language.
+
+    This dependency returns a translation function that automatically
+    uses the current request's language, making it easy to translate
+    strings in route handlers.
+
+    Args:
+        request: FastAPI request object
+
+    Returns:
+        Translation function with signature: t(key: str, **params) -> str
+
+    Usage:
+        @router.post("/workspaces")
+        async def create_workspace(
+            data: WorkspaceCreate,
+            t: Callable = Depends(get_translator)
+        ):
+            workspace = await workspace_service.create(data)
+            return {
+                "success": True,
+                "message": t("workspace.created_successfully"),
+                "data": workspace
+            }
+
+        # With parameters
+        @router.get("/items")
+        async def get_items(t: Callable = Depends(get_translator)):
+            count = 5
+            return {
+                "message": t("items.found", count=count)
+            }
+    """
+    # Get current language
+    language = await get_current_language(request)
+
+    # Get translation service
+    service = get_translation_service()
+
+    # Return a bound translation function
+    def translate(key: str, **params) -> str:
+        """
+        Translate a key using the current request's language.
+
+        Args:
+            key: Translation key (e.g., "common.success.created")
+            **params: Parameters for parameterized messages
+
+        Returns:
+            Translated string
+        """
+        return service.translate(key, language, **params)
+
+    return translate
+
+
+async def get_enum_translator(request: Request) -> Callable:
+    """
+    Get an enum translator function bound to the current request's language.
+
+    This dependency returns a function for translating enum values
+    that automatically uses the current request's language.
+
+    Args:
+        request: FastAPI request object
+
+    Returns:
+        Enum translation function with signature:
+        t_enum(enum_type: str, value: str) -> str
+
+    Usage:
+        @router.get("/workspace/{id}")
+        async def get_workspace(
+            id: str,
+            t_enum: Callable = Depends(get_enum_translator)
+        ):
+            workspace = await workspace_service.get(id)
+            return {
+                "id": workspace.id,
+                "role": workspace.role,
+                "role_display": t_enum("workspace_role", workspace.role),
+                "status": workspace.status,
+                "status_display": t_enum("workspace_status", workspace.status)
+            }
+    """
+    # Get current language
+    language = await get_current_language(request)
+
+    # Get translation service
+    service = get_translation_service()
+
+    # Return a bound enum translation function
+    def translate_enum(enum_type: str, value: str) -> str:
+        """
+        Translate an enum value using the current request's language.
+
+        Args:
+            enum_type: Enum type name (e.g., "workspace_role")
+            value: Enum value (e.g., "manager")
+
+        Returns:
+            Translated enum display name
+        """
+        return service.translate_enum(enum_type, value, language)
+
+    return translate_enum

api/app/i18n/exceptions.py

@@ -0,0 +1,495 @@
+"""
+Internationalized exception classes for i18n system.
+
+This module provides exception classes that automatically translate
+error messages based on the current request's language.
+"""
+
+import logging
+from contextvars import ContextVar
+from typing import Any, Dict, Optional
+
+from fastapi import HTTPException, Request
+
+from app.i18n.service import get_translation_service
+
+logger = logging.getLogger(__name__)
+
+# Context variable to store current locale
+_current_locale: ContextVar[Optional[str]] = ContextVar("current_locale", default=None)
+
+
+def set_current_locale(locale: str) -> None:
+    """
+    Set the current locale in the context variable.
+    
+    This should be called by the LanguageMiddleware.
+    
+    Args:
+        locale: Locale code (e.g., "zh", "en")
+    """
+    _current_locale.set(locale)
+
+
+def get_current_locale() -> Optional[str]:
+    """
+    Get the current locale from the context variable.
+    
+    Returns:
+        Locale code or None if not set
+    """
+    return _current_locale.get()
+
+
+class I18nException(HTTPException):
+    """
+    Base exception class with automatic i18n support.
+
+    This exception automatically translates error messages based on:
+    1. The current request's language (from request.state.language)
+    2. The fallback language if request language is not available
+    3. The error key itself if no translation is found
+
+    Features:
+    - Automatic error message translation
+    - Parameterized error messages support
+    - Consistent error response format
+    - Language-aware error handling
+
+    Usage:
+        # Simple error
+        raise I18nException(
+            error_key="errors.workspace.not_found",
+            status_code=404
+        )
+
+        # Error with parameters
+        raise I18nException(
+            error_key="errors.validation.missing_field",
+            status_code=400,
+            field="name"
+        )
+
+        # Custom error code
+        raise I18nException(
+            error_key="errors.workspace.not_found",
+            error_code="WORKSPACE_NOT_FOUND",
+            status_code=404,
+            workspace_id="123"
+        )
+    """
+
+    def __init__(
+        self,
+        error_key: str,
+        status_code: int = 400,
+        error_code: Optional[str] = None,
+        locale: Optional[str] = None,
+        headers: Optional[Dict[str, str]] = None,
+        **params
+    ):
+        """
+        Initialize the i18n exception.
+
+        Args:
+            error_key: Translation key for the error message
+                      (e.g., "errors.workspace.not_found")
+            status_code: HTTP status code (default: 400)
+            error_code: Custom error code for API clients
+                       (default: derived from error_key)
+            locale: Target locale for translation (optional)
+                   If not provided, uses current request's language
+            headers: Additional HTTP headers
+            **params: Parameters for parameterized error messages
+        """
+        self.error_key = error_key
+        self.error_code = error_code or self._generate_error_code(error_key)
+        self.params = params
+
+        # Get locale from request context if not provided
+        if locale is None:
+            locale = self._get_current_locale()
+
+        # Translate error message
+        translation_service = get_translation_service()
+        message = translation_service.translate(
+            error_key,
+            locale,
+            **params
+        )
+
+        # Build error detail
+        detail = {
+            "error_code": self.error_code,
+            "message": message,
+        }
+
+        # Add parameters to detail if provided
+        if params:
+            detail["params"] = params
+
+        # Initialize HTTPException
+        super().__init__(
+            status_code=status_code,
+            detail=detail,
+            headers=headers
+        )
+
+        logger.debug(
+            f"I18nException raised: {self.error_code} "
+            f"(key: {error_key}, locale: {locale})"
+        )
+
+    def _get_current_locale(self) -> str:
+        """
+        Get the current locale from request context.
+
+        Returns:
+            Locale code (e.g., "zh", "en")
+        """
+        try:
+            # Try to get locale from context variable
+            locale = _current_locale.get()
+            if locale:
+                return locale
+        except Exception as e:
+            logger.debug(f"Could not get locale from context: {e}")
+
+        # Fallback to default locale
+        from app.core.config import settings
+        return settings.I18N_DEFAULT_LANGUAGE
+
+    def _generate_error_code(self, error_key: str) -> str:
+        """
+        Generate error code from error key.
+
+        Converts "errors.workspace.not_found" to "WORKSPACE_NOT_FOUND"
+
+        Args:
+            error_key: Translation key
+
+        Returns:
+            Error code in UPPER_SNAKE_CASE
+        """
+        # Remove "errors." prefix if present
+        if error_key.startswith("errors."):
+            error_key = error_key[7:]
+
+        # Convert to UPPER_SNAKE_CASE
+        parts = error_key.split(".")
+        return "_".join(parts).upper()
+
+
+# Specific exception classes for common errors
+
+class BadRequestError(I18nException):
+    """Bad request error (400)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.common.bad_request",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=400,
+            error_code=error_code,
+            **params
+        )
+
+
+class UnauthorizedError(I18nException):
+    """Unauthorized error (401)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.auth.unauthorized",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=401,
+            error_code=error_code,
+            **params
+        )
+
+
+class ForbiddenError(I18nException):
+    """Forbidden error (403)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.auth.forbidden",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=403,
+            error_code=error_code,
+            **params
+        )
+
+
+class NotFoundError(I18nException):
+    """Not found error (404)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.common.not_found",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=404,
+            error_code=error_code,
+            **params
+        )
+
+
+class ConflictError(I18nException):
+    """Conflict error (409)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.common.conflict",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=409,
+            error_code=error_code,
+            **params
+        )
+
+
+class ValidationError(I18nException):
+    """Validation error (422)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.common.validation_failed",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=422,
+            error_code=error_code,
+            **params
+        )
+
+
+class InternalServerError(I18nException):
+    """Internal server error (500)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.common.internal_error",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=500,
+            error_code=error_code,
+            **params
+        )
+
+
+class ServiceUnavailableError(I18nException):
+    """Service unavailable error (503)."""
+
+    def __init__(
+        self,
+        error_key: str = "errors.common.service_unavailable",
+        error_code: Optional[str] = None,
+        **params
+    ):
+        super().__init__(
+            error_key=error_key,
+            status_code=503,
+            error_code=error_code,
+            **params
+        )
+
+
+# Domain-specific exception classes
+
+class WorkspaceNotFoundError(NotFoundError):
+    """Workspace not found error."""
+
+    def __init__(self, workspace_id: Optional[str] = None, **params):
+        if workspace_id:
+            params["workspace_id"] = workspace_id
+        super().__init__(
+            error_key="errors.workspace.not_found",
+            error_code="WORKSPACE_NOT_FOUND",
+            **params
+        )
+
+
+class WorkspacePermissionDeniedError(ForbiddenError):
+    """Workspace permission denied error."""
+
+    def __init__(self, workspace_id: Optional[str] = None, **params):
+        if workspace_id:
+            params["workspace_id"] = workspace_id
+        super().__init__(
+            error_key="errors.workspace.permission_denied",
+            error_code="WORKSPACE_PERMISSION_DENIED",
+            **params
+        )
+
+
+class UserNotFoundError(NotFoundError):
+    """User not found error."""
+
+    def __init__(self, user_id: Optional[str] = None, **params):
+        if user_id:
+            params["user_id"] = user_id
+        super().__init__(
+            error_key="errors.user.not_found",
+            error_code="USER_NOT_FOUND",
+            **params
+        )
+
+
+class UserAlreadyExistsError(ConflictError):
+    """User already exists error."""
+
+    def __init__(self, identifier: Optional[str] = None, **params):
+        if identifier:
+            params["identifier"] = identifier
+        super().__init__(
+            error_key="errors.user.already_exists",
+            error_code="USER_ALREADY_EXISTS",
+            **params
+        )
+
+
+class TenantNotFoundError(NotFoundError):
+    """Tenant not found error."""
+
+    def __init__(self, tenant_id: Optional[str] = None, **params):
+        if tenant_id:
+            params["tenant_id"] = tenant_id
+        super().__init__(
+            error_key="errors.tenant.not_found",
+            error_code="TENANT_NOT_FOUND",
+            **params
+        )
+
+
+class TenantSuspendedError(ForbiddenError):
+    """Tenant suspended error."""
+
+    def __init__(self, tenant_id: Optional[str] = None, **params):
+        if tenant_id:
+            params["tenant_id"] = tenant_id
+        super().__init__(
+            error_key="errors.tenant.suspended",
+            error_code="TENANT_SUSPENDED",
+            **params
+        )
+
+
+class InvalidCredentialsError(UnauthorizedError):
+    """Invalid credentials error."""
+
+    def __init__(self, **params):
+        super().__init__(
+            error_key="errors.auth.invalid_credentials",
+            error_code="INVALID_CREDENTIALS",
+            **params
+        )
+
+
+class TokenExpiredError(UnauthorizedError):
+    """Token expired error."""
+
+    def __init__(self, **params):
+        super().__init__(
+            error_key="errors.auth.token_expired",
+            error_code="TOKEN_EXPIRED",
+            **params
+        )
+
+
+class TokenInvalidError(UnauthorizedError):
+    """Token invalid error."""
+
+    def __init__(self, **params):
+        super().__init__(
+            error_key="errors.auth.token_invalid",
+            error_code="TOKEN_INVALID",
+            **params
+        )
+
+
+class FileNotFoundError(NotFoundError):
+    """File not found error."""
+
+    def __init__(self, file_id: Optional[str] = None, **params):
+        if file_id:
+            params["file_id"] = file_id
+        super().__init__(
+            error_key="errors.file.not_found",
+            error_code="FILE_NOT_FOUND",
+            **params
+        )
+
+
+class FileTooLargeError(BadRequestError):
+    """File too large error."""
+
+    def __init__(self, max_size: Optional[str] = None, **params):
+        if max_size:
+            params["max_size"] = max_size
+        super().__init__(
+            error_key="errors.file.too_large",
+            error_code="FILE_TOO_LARGE",
+            **params
+        )
+
+
+class InvalidFileTypeError(BadRequestError):
+    """Invalid file type error."""
+
+    def __init__(self, file_type: Optional[str] = None, **params):
+        if file_type:
+            params["file_type"] = file_type
+        super().__init__(
+            error_key="errors.file.invalid_type",
+            error_code="INVALID_FILE_TYPE",
+            **params
+        )
+
+
+class RateLimitExceededError(I18nException):
+    """Rate limit exceeded error (429)."""
+
+    def __init__(self, **params):
+        super().__init__(
+            error_key="errors.api.rate_limit_exceeded",
+            status_code=429,
+            error_code="RATE_LIMIT_EXCEEDED",
+            **params
+        )
+
+
+class QuotaExceededError(ForbiddenError):
+    """Quota exceeded error."""
+
+    def __init__(self, resource: Optional[str] = None, **params):
+        if resource:
+            params["resource"] = resource
+        super().__init__(
+            error_key="errors.api.quota_exceeded",
+            error_code="QUOTA_EXCEEDED",
+            **params
+        )

api/app/i18n/loader.py

@@ -0,0 +1,199 @@
+"""
+Translation file loader for i18n system.
+
+This module handles loading translation files from multiple directories
+(community edition + enterprise edition) and provides hot reload support.
+"""
+
+import json
+import logging
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+logger = logging.getLogger(__name__)
+
+
+class TranslationLoader:
+    """
+    Translation file loader that supports:
+    - Loading from multiple directories (community + enterprise)
+    - Hot reload of translation files
+    - Automatic locale detection
+    """
+
+    def __init__(self, locales_dirs: Optional[List[str]] = None):
+        """
+        Initialize the translation loader.
+
+        Args:
+            locales_dirs: List of directories containing translation files.
+                         If None, will auto-detect from settings.
+        """
+        if locales_dirs is None:
+            locales_dirs = self._detect_locales_dirs()
+
+        self.locales_dirs = [Path(d) for d in locales_dirs]
+        logger.info(f"TranslationLoader initialized with directories: {self.locales_dirs}")
+
+    def _detect_locales_dirs(self) -> List[str]:
+        """
+        Auto-detect translation directories from settings.
+
+        Returns:
+            List of translation directory paths
+        """
+        from app.core.config import settings
+
+        dirs = []
+
+        # 1. Core locales directory (community edition, required)
+        core_dir = Path(settings.I18N_CORE_LOCALES_DIR)
+        if core_dir.exists():
+            dirs.append(str(core_dir))
+            logger.debug(f"Found core locales directory: {core_dir}")
+        else:
+            logger.warning(f"Core locales directory not found: {core_dir}")
+
+        # 2. Premium locales directory (enterprise edition, optional)
+        if settings.I18N_PREMIUM_LOCALES_DIR:
+            premium_dir = Path(settings.I18N_PREMIUM_LOCALES_DIR)
+            if premium_dir.exists():
+                dirs.append(str(premium_dir))
+                logger.debug(f"Found premium locales directory: {premium_dir}")
+        else:
+            # Auto-detect premium directory
+            premium_dir = Path("premium/locales")
+            if premium_dir.exists():
+                dirs.append(str(premium_dir))
+                logger.debug(f"Auto-detected premium locales directory: {premium_dir}")
+
+        if not dirs:
+            logger.error("No translation directories found!")
+
+        return dirs
+
+    def get_available_locales(self) -> List[str]:
+        """
+        Get list of all available locales across all directories.
+
+        Returns:
+            List of locale codes (e.g., ['zh', 'en'])
+        """
+        locales = set()
+
+        for locales_dir in self.locales_dirs:
+            if not locales_dir.exists():
+                continue
+
+            for locale_dir in locales_dir.iterdir():
+                if locale_dir.is_dir() and not locale_dir.name.startswith('.'):
+                    locales.add(locale_dir.name)
+
+        return sorted(list(locales))
+
+    def load_locale(self, locale: str) -> Dict[str, Any]:
+        """
+        Load all translation files for a specific locale from all directories.
+
+        Translation files are merged with priority:
+        - Later directories override earlier directories
+        - Enterprise translations override community translations
+
+        Args:
+            locale: Locale code (e.g., 'zh', 'en')
+
+        Returns:
+            Dictionary of translations organized by namespace
+            Format: {namespace: {key: value, ...}, ...}
+        """
+        translations = {}
+
+        # Load from each directory in order (later directories override earlier)
+        for locales_dir in self.locales_dirs:
+            locale_dir = locales_dir / locale
+            if not locale_dir.exists():
+                logger.debug(f"Locale directory not found: {locale_dir}")
+                continue
+
+            # Load all JSON files in this locale directory
+            for json_file in locale_dir.glob("*.json"):
+                namespace = json_file.stem
+
+                try:
+                    with open(json_file, "r", encoding="utf-8") as f:
+                        new_translations = json.load(f)
+
+                    # Merge translations (deep merge)
+                    if namespace in translations:
+                        translations[namespace] = self._deep_merge(
+                            translations[namespace],
+                            new_translations
+                        )
+                        logger.debug(
+                            f"Merged translations: {locale}/{namespace} from {json_file}"
+                        )
+                    else:
+                        translations[namespace] = new_translations
+                        logger.debug(
+                            f"Loaded translations: {locale}/{namespace} from {json_file}"
+                        )
+
+                except json.JSONDecodeError as e:
+                    logger.error(
+                        f"Failed to parse JSON file {json_file}: {e}"
+                    )
+                except Exception as e:
+                    logger.error(
+                        f"Failed to load translation file {json_file}: {e}"
+                    )
+
+        if not translations:
+            logger.warning(f"No translations found for locale: {locale}")
+
+        return translations
+
+    def reload(self, locale: Optional[str] = None) -> Dict[str, Dict[str, Any]]:
+        """
+        Reload translation files.
+
+        Args:
+            locale: Specific locale to reload. If None, reloads all locales.
+
+        Returns:
+            Dictionary of reloaded translations
+            Format: {locale: {namespace: {key: value}}}
+        """
+        if locale:
+            logger.info(f"Reloading translations for locale: {locale}")
+            return {locale: self.load_locale(locale)}
+        else:
+            logger.info("Reloading all translations")
+            all_translations = {}
+            for loc in self.get_available_locales():
+                all_translations[loc] = self.load_locale(loc)
+            return all_translations
+
+    def _deep_merge(self, base: Dict, override: Dict) -> Dict:
+        """
+        Deep merge two dictionaries.
+
+        Args:
+            base: Base dictionary
+            override: Dictionary with values to override
+
+        Returns:
+            Merged dictionary
+        """
+        result = base.copy()
+
+        for key, value in override.items():
+            if (
+                key in result
+                and isinstance(result[key], dict)
+                and isinstance(value, dict)
+            ):
+                result[key] = self._deep_merge(result[key], value)
+            else:
+                result[key] = value
+
+        return result

api/app/i18n/logger.py

@@ -0,0 +1,382 @@
+"""
+Translation logging for i18n system.
+
+This module provides:
+- TranslationLogger for recording missing translations
+- Missing translation report generation
+- Integration with existing logging system
+- Structured logging for translation events
+"""
+
+import logging
+from typing import Dict, List, Optional, Set
+from datetime import datetime
+from collections import defaultdict
+from pathlib import Path
+import json
+
+from app.core.logging_config import get_logger
+
+logger = get_logger(__name__)
+
+
+class TranslationLogger:
+    """
+    Logger for translation events and missing translations.
+    
+    Features:
+    - Records missing translations with context
+    - Generates missing translation reports
+    - Integrates with existing logging system
+    - Provides structured logging for analysis
+    """
+    
+    def __init__(self, log_file: Optional[str] = None):
+        """
+        Initialize translation logger.
+        
+        Args:
+            log_file: Optional custom log file path for missing translations
+        """
+        self.log_file = log_file or "logs/i18n/missing_translations.log"
+        self._missing_translations: Dict[str, Set[str]] = defaultdict(set)
+        self._missing_with_context: List[Dict] = []
+        self._max_context_entries = 10000  # Keep last 10k entries
+        
+        # Ensure log directory exists
+        log_path = Path(self.log_file)
+        log_path.parent.mkdir(parents=True, exist_ok=True)
+        
+        # Create dedicated file handler for missing translations
+        self._file_handler = logging.FileHandler(
+            self.log_file,
+            encoding='utf-8'
+        )
+        self._file_handler.setLevel(logging.WARNING)
+        
+        # Create formatter
+        formatter = logging.Formatter(
+            fmt='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
+            datefmt='%Y-%m-%d %H:%M:%S'
+        )
+        self._file_handler.setFormatter(formatter)
+        
+        # Create dedicated logger for missing translations
+        self._logger = logging.getLogger("i18n.missing_translations")
+        self._logger.setLevel(logging.WARNING)
+        self._logger.addHandler(self._file_handler)
+        self._logger.propagate = False  # Don't propagate to root logger
+        
+        logger.info(f"TranslationLogger initialized with log file: {self.log_file}")
+    
+    def log_missing_translation(
+        self,
+        key: str,
+        locale: str,
+        context: Optional[Dict] = None
+    ):
+        """
+        Log a missing translation.
+        
+        Args:
+            key: Translation key that was not found
+            locale: Locale code
+            context: Optional context information (e.g., request path, user info)
+        """
+        # Add to missing set
+        self._missing_translations[locale].add(key)
+        
+        # Create context entry
+        entry = {
+            "timestamp": datetime.now().isoformat(),
+            "key": key,
+            "locale": locale,
+            "context": context or {}
+        }
+        
+        # Keep only recent entries to avoid memory bloat
+        if len(self._missing_with_context) >= self._max_context_entries:
+            self._missing_with_context.pop(0)
+        
+        self._missing_with_context.append(entry)
+        
+        # Log to file
+        context_str = f" (context: {context})" if context else ""
+        self._logger.warning(
+            f"Missing translation: key='{key}', locale='{locale}'{context_str}"
+        )
+    
+    def log_translation_error(
+        self,
+        error_type: str,
+        message: str,
+        key: Optional[str] = None,
+        locale: Optional[str] = None,
+        context: Optional[Dict] = None
+    ):
+        """
+        Log a translation error.
+        
+        Args:
+            error_type: Type of error (e.g., "format_error", "parameter_missing")
+            message: Error message
+            key: Translation key (optional)
+            locale: Locale code (optional)
+            context: Optional context information
+        """
+        error_data = {
+            "error_type": error_type,
+            "message": message,
+            "key": key,
+            "locale": locale,
+            "context": context or {},
+            "timestamp": datetime.now().isoformat()
+        }
+        
+        self._logger.error(
+            f"Translation error: {error_type} - {message} "
+            f"(key: {key}, locale: {locale})"
+        )
+    
+    def log_translation_success(
+        self,
+        key: str,
+        locale: str,
+        duration_ms: Optional[float] = None
+    ):
+        """
+        Log a successful translation (debug level).
+        
+        Args:
+            key: Translation key
+            locale: Locale code
+            duration_ms: Optional duration in milliseconds
+        """
+        duration_str = f" ({duration_ms:.3f}ms)" if duration_ms else ""
+        logger.debug(
+            f"Translation success: key='{key}', locale='{locale}'{duration_str}"
+        )
+    
+    def get_missing_translations(
+        self,
+        locale: Optional[str] = None
+    ) -> Dict[str, List[str]]:
+        """
+        Get missing translations.
+        
+        Args:
+            locale: Specific locale (optional, returns all if None)
+            
+        Returns:
+            Dictionary of missing translations by locale
+        """
+        if locale:
+            return {locale: sorted(list(self._missing_translations.get(locale, set())))}
+        
+        return {
+            loc: sorted(list(keys))
+            for loc, keys in self._missing_translations.items()
+        }
+    
+    def get_missing_with_context(
+        self,
+        locale: Optional[str] = None,
+        limit: Optional[int] = None
+    ) -> List[Dict]:
+        """
+        Get missing translations with context.
+        
+        Args:
+            locale: Filter by locale (optional)
+            limit: Maximum number of entries to return (optional)
+            
+        Returns:
+            List of missing translation entries with context
+        """
+        entries = self._missing_with_context
+        
+        # Filter by locale if specified
+        if locale:
+            entries = [e for e in entries if e["locale"] == locale]
+        
+        # Apply limit if specified
+        if limit:
+            entries = entries[-limit:]
+        
+        return entries
+    
+    def generate_report(
+        self,
+        locale: Optional[str] = None,
+        output_file: Optional[str] = None
+    ) -> Dict:
+        """
+        Generate a missing translation report.
+        
+        Args:
+            locale: Specific locale (optional, generates for all if None)
+            output_file: Optional file path to save report as JSON
+            
+        Returns:
+            Report dictionary
+        """
+        missing = self.get_missing_translations(locale)
+        
+        report = {
+            "generated_at": datetime.now().isoformat(),
+            "total_missing": sum(len(keys) for keys in missing.values()),
+            "missing_by_locale": {
+                loc: {
+                    "count": len(keys),
+                    "keys": keys
+                }
+                for loc, keys in missing.items()
+            },
+            "recent_context": self.get_missing_with_context(locale, limit=100)
+        }
+        
+        # Save to file if specified
+        if output_file:
+            output_path = Path(output_file)
+            output_path.parent.mkdir(parents=True, exist_ok=True)
+            
+            with open(output_path, 'w', encoding='utf-8') as f:
+                json.dump(report, f, indent=2, ensure_ascii=False)
+            
+            logger.info(f"Missing translation report saved to: {output_file}")
+        
+        return report
+    
+    def get_statistics(self) -> Dict:
+        """
+        Get statistics about missing translations.
+        
+        Returns:
+            Dictionary with statistics
+        """
+        total_missing = sum(len(keys) for keys in self._missing_translations.values())
+        
+        # Count by namespace
+        namespace_counts = defaultdict(int)
+        for locale, keys in self._missing_translations.items():
+            for key in keys:
+                namespace = key.split('.')[0] if '.' in key else 'unknown'
+                namespace_counts[namespace] += 1
+        
+        return {
+            "total_missing": total_missing,
+            "locales_affected": len(self._missing_translations),
+            "missing_by_locale": {
+                loc: len(keys)
+                for loc, keys in self._missing_translations.items()
+            },
+            "missing_by_namespace": dict(namespace_counts),
+            "total_context_entries": len(self._missing_with_context)
+        }
+    
+    def clear(self, locale: Optional[str] = None):
+        """
+        Clear missing translation records.
+        
+        Args:
+            locale: Specific locale to clear (optional, clears all if None)
+        """
+        if locale:
+            self._missing_translations.pop(locale, None)
+            self._missing_with_context = [
+                e for e in self._missing_with_context
+                if e["locale"] != locale
+            ]
+            logger.info(f"Cleared missing translations for locale: {locale}")
+        else:
+            self._missing_translations.clear()
+            self._missing_with_context.clear()
+            logger.info("Cleared all missing translations")
+    
+    def export_to_json(self, output_file: str):
+        """
+        Export all missing translations to JSON file.
+        
+        Args:
+            output_file: Output file path
+        """
+        data = {
+            "exported_at": datetime.now().isoformat(),
+            "missing_translations": self.get_missing_translations(),
+            "statistics": self.get_statistics(),
+            "recent_context": self.get_missing_with_context(limit=1000)
+        }
+        
+        output_path = Path(output_file)
+        output_path.parent.mkdir(parents=True, exist_ok=True)
+        
+        with open(output_path, 'w', encoding='utf-8') as f:
+            json.dump(data, f, indent=2, ensure_ascii=False)
+        
+        logger.info(f"Missing translations exported to: {output_file}")
+    
+    def __del__(self):
+        """Cleanup file handler on deletion."""
+        try:
+            if hasattr(self, '_file_handler'):
+                self._file_handler.close()
+                self._logger.removeHandler(self._file_handler)
+        except Exception:
+            pass
+
+
+# Global translation logger instance
+_translation_logger: Optional[TranslationLogger] = None
+
+
+def get_translation_logger() -> TranslationLogger:
+    """
+    Get the global translation logger instance.
+    
+    Returns:
+        TranslationLogger singleton
+    """
+    global _translation_logger
+    if _translation_logger is None:
+        _translation_logger = TranslationLogger()
+    return _translation_logger
+
+
+def log_missing_translation(
+    key: str,
+    locale: str,
+    context: Optional[Dict] = None
+):
+    """
+    Log a missing translation (convenience function).
+    
+    Args:
+        key: Translation key
+        locale: Locale code
+        context: Optional context information
+    """
+    translation_logger = get_translation_logger()
+    translation_logger.log_missing_translation(key, locale, context)
+
+
+def log_translation_error(
+    error_type: str,
+    message: str,
+    key: Optional[str] = None,
+    locale: Optional[str] = None,
+    context: Optional[Dict] = None
+):
+    """
+    Log a translation error (convenience function).
+    
+    Args:
+        error_type: Type of error
+        message: Error message
+        key: Translation key (optional)
+        locale: Locale code (optional)
+        context: Optional context information
+    """
+    translation_logger = get_translation_logger()
+    translation_logger.log_translation_error(
+        error_type, message, key, locale, context
+    )

api/app/i18n/metrics.py

@@ -0,0 +1,337 @@
+"""
+Performance monitoring and metrics for i18n system.
+
+This module provides:
+- Translation request counters
+- Translation timing metrics
+- Missing translation tracking
+- Performance monitoring decorators
+- Prometheus-compatible metrics
+"""
+
+import logging
+import time
+from functools import wraps
+from typing import Any, Callable, Dict, Optional
+from collections import defaultdict
+from datetime import datetime
+
+logger = logging.getLogger(__name__)
+
+
+class TranslationMetrics:
+    """
+    Metrics collector for translation operations.
+    
+    Tracks:
+    - Translation request counts
+    - Translation timing (latency)
+    - Missing translations
+    - Cache performance
+    - Locale usage
+    """
+    
+    def __init__(self):
+        """Initialize metrics collector."""
+        # Request counters by locale
+        self._request_counts: Dict[str, int] = defaultdict(int)
+        
+        # Missing translation tracker
+        self._missing_translations: Dict[str, set] = defaultdict(set)
+        
+        # Timing metrics (in milliseconds)
+        self._timing_data: list = []
+        self._max_timing_samples = 10000  # Keep last 10k samples
+        
+        # Locale usage
+        self._locale_usage: Dict[str, int] = defaultdict(int)
+        
+        # Namespace usage
+        self._namespace_usage: Dict[str, int] = defaultdict(int)
+        
+        # Error counts
+        self._error_counts: Dict[str, int] = defaultdict(int)
+        
+        # Start time
+        self._start_time = datetime.now()
+        
+        logger.info("TranslationMetrics initialized")
+    
+    def record_request(self, locale: str, namespace: str = None):
+        """
+        Record a translation request.
+        
+        Args:
+            locale: Locale code
+            namespace: Translation namespace (optional)
+        """
+        self._request_counts[locale] += 1
+        self._locale_usage[locale] += 1
+        
+        if namespace:
+            self._namespace_usage[namespace] += 1
+    
+    def record_missing(self, key: str, locale: str):
+        """
+        Record a missing translation.
+        
+        Args:
+            key: Translation key
+            locale: Locale code
+        """
+        self._missing_translations[locale].add(key)
+        logger.debug(f"Missing translation recorded: {key} (locale: {locale})")
+    
+    def record_timing(self, duration_ms: float, locale: str, operation: str = "translate"):
+        """
+        Record translation operation timing.
+        
+        Args:
+            duration_ms: Duration in milliseconds
+            locale: Locale code
+            operation: Operation type
+        """
+        # Keep only recent samples to avoid memory bloat
+        if len(self._timing_data) >= self._max_timing_samples:
+            self._timing_data.pop(0)
+        
+        self._timing_data.append({
+            "duration_ms": duration_ms,
+            "locale": locale,
+            "operation": operation,
+            "timestamp": time.time()
+        })
+    
+    def record_error(self, error_type: str):
+        """
+        Record an error.
+        
+        Args:
+            error_type: Type of error
+        """
+        self._error_counts[error_type] += 1
+    
+    def get_summary(self) -> Dict[str, Any]:
+        """
+        Get metrics summary.
+        
+        Returns:
+            Dictionary with metrics summary
+        """
+        total_requests = sum(self._request_counts.values())
+        total_missing = sum(len(keys) for keys in self._missing_translations.values())
+        
+        # Calculate timing statistics
+        timing_stats = self._calculate_timing_stats()
+        
+        # Calculate uptime
+        uptime_seconds = (datetime.now() - self._start_time).total_seconds()
+        
+        return {
+            "uptime_seconds": round(uptime_seconds, 2),
+            "total_requests": total_requests,
+            "requests_per_locale": dict(self._request_counts),
+            "total_missing_translations": total_missing,
+            "missing_by_locale": {
+                locale: len(keys)
+                for locale, keys in self._missing_translations.items()
+            },
+            "timing": timing_stats,
+            "locale_usage": dict(self._locale_usage),
+            "namespace_usage": dict(self._namespace_usage),
+            "error_counts": dict(self._error_counts)
+        }
+    
+    def _calculate_timing_stats(self) -> Dict[str, Any]:
+        """
+        Calculate timing statistics.
+        
+        Returns:
+            Dictionary with timing statistics
+        """
+        if not self._timing_data:
+            return {
+                "count": 0,
+                "avg_ms": 0,
+                "min_ms": 0,
+                "max_ms": 0,
+                "p50_ms": 0,
+                "p95_ms": 0,
+                "p99_ms": 0
+            }
+        
+        durations = [d["duration_ms"] for d in self._timing_data]
+        durations.sort()
+        
+        count = len(durations)
+        avg = sum(durations) / count
+        
+        # Calculate percentiles
+        p50_idx = int(count * 0.50)
+        p95_idx = int(count * 0.95)
+        p99_idx = int(count * 0.99)
+        
+        return {
+            "count": count,
+            "avg_ms": round(avg, 3),
+            "min_ms": round(durations[0], 3),
+            "max_ms": round(durations[-1], 3),
+            "p50_ms": round(durations[p50_idx], 3),
+            "p95_ms": round(durations[p95_idx], 3),
+            "p99_ms": round(durations[p99_idx], 3)
+        }
+    
+    def get_missing_translations(self, locale: Optional[str] = None) -> Dict[str, list]:
+        """
+        Get missing translations.
+        
+        Args:
+            locale: Specific locale (optional, returns all if None)
+            
+        Returns:
+            Dictionary of missing translations by locale
+        """
+        if locale:
+            return {locale: list(self._missing_translations.get(locale, set()))}
+        
+        return {
+            locale: list(keys)
+            for locale, keys in self._missing_translations.items()
+        }
+    
+    def reset(self):
+        """Reset all metrics."""
+        self._request_counts.clear()
+        self._missing_translations.clear()
+        self._timing_data.clear()
+        self._locale_usage.clear()
+        self._namespace_usage.clear()
+        self._error_counts.clear()
+        self._start_time = datetime.now()
+        logger.info("Metrics reset")
+    
+    def export_prometheus(self) -> str:
+        """
+        Export metrics in Prometheus format.
+        
+        Returns:
+            Prometheus-formatted metrics string
+        """
+        lines = []
+        
+        # Translation requests counter
+        lines.append("# HELP i18n_translation_requests_total Total number of translation requests")
+        lines.append("# TYPE i18n_translation_requests_total counter")
+        for locale, count in self._request_counts.items():
+            lines.append(f'i18n_translation_requests_total{{locale="{locale}"}} {count}')
+        
+        # Missing translations counter
+        lines.append("# HELP i18n_missing_translations_total Total number of missing translations")
+        lines.append("# TYPE i18n_missing_translations_total counter")
+        for locale, keys in self._missing_translations.items():
+            lines.append(f'i18n_missing_translations_total{{locale="{locale}"}} {len(keys)}')
+        
+        # Timing metrics
+        timing_stats = self._calculate_timing_stats()
+        lines.append("# HELP i18n_translation_duration_ms Translation operation duration in milliseconds")
+        lines.append("# TYPE i18n_translation_duration_ms summary")
+        lines.append(f'i18n_translation_duration_ms{{quantile="0.5"}} {timing_stats["p50_ms"]}')
+        lines.append(f'i18n_translation_duration_ms{{quantile="0.95"}} {timing_stats["p95_ms"]}')
+        lines.append(f'i18n_translation_duration_ms{{quantile="0.99"}} {timing_stats["p99_ms"]}')
+        lines.append(f'i18n_translation_duration_ms_sum {sum(d["duration_ms"] for d in self._timing_data)}')
+        lines.append(f'i18n_translation_duration_ms_count {timing_stats["count"]}')
+        
+        # Error counter
+        lines.append("# HELP i18n_errors_total Total number of i18n errors")
+        lines.append("# TYPE i18n_errors_total counter")
+        for error_type, count in self._error_counts.items():
+            lines.append(f'i18n_errors_total{{type="{error_type}"}} {count}')
+        
+        return "\n".join(lines)
+
+
+# Global metrics instance
+_metrics: Optional[TranslationMetrics] = None
+
+
+def get_metrics() -> TranslationMetrics:
+    """
+    Get the global metrics instance.
+    
+    Returns:
+        TranslationMetrics singleton
+    """
+    global _metrics
+    if _metrics is None:
+        _metrics = TranslationMetrics()
+    return _metrics
+
+
+def monitor_performance(operation: str = "translate"):
+    """
+    Decorator to monitor translation operation performance.
+    
+    Args:
+        operation: Operation name for metrics
+        
+    Returns:
+        Decorated function
+        
+    Example:
+        @monitor_performance("translate")
+        def translate(key: str, locale: str) -> str:
+            ...
+    """
+    def decorator(func: Callable) -> Callable:
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            start_time = time.perf_counter()
+            
+            try:
+                result = func(*args, **kwargs)
+                
+                # Record timing
+                duration_ms = (time.perf_counter() - start_time) * 1000
+                
+                # Try to extract locale from args/kwargs
+                locale = kwargs.get("locale", "unknown")
+                if not locale and len(args) > 1:
+                    locale = args[1] if isinstance(args[1], str) else "unknown"
+                
+                metrics = get_metrics()
+                metrics.record_timing(duration_ms, locale, operation)
+                
+                return result
+            
+            except Exception as e:
+                # Record error
+                metrics = get_metrics()
+                metrics.record_error(type(e).__name__)
+                raise
+        
+        return wrapper
+    return decorator
+
+
+def track_missing_translation(key: str, locale: str):
+    """
+    Track a missing translation.
+    
+    Args:
+        key: Translation key
+        locale: Locale code
+    """
+    metrics = get_metrics()
+    metrics.record_missing(key, locale)
+
+
+def track_translation_request(locale: str, namespace: str = None):
+    """
+    Track a translation request.
+    
+    Args:
+        locale: Locale code
+        namespace: Translation namespace (optional)
+    """
+    metrics = get_metrics()
+    metrics.record_request(locale, namespace)

api/app/i18n/middleware.py

@@ -0,0 +1,202 @@
+"""
+Language detection middleware for i18n system.
+
+This middleware determines the language to use for each request based on:
+1. Query parameter (?lang=en)
+2. Accept-Language HTTP header
+3. User language preference (from database)
+4. Tenant default language
+5. System default language
+
+The detected language is injected into request.state.language and
+added to the response Content-Language header.
+"""
+
+import logging
+import re
+from typing import Optional
+
+from fastapi import Request
+from starlette.middleware.base import BaseHTTPMiddleware
+
+logger = logging.getLogger(__name__)
+
+
+class LanguageMiddleware(BaseHTTPMiddleware):
+    """
+    Language detection middleware.
+    
+    Determines the language for each request based on multiple sources
+    with a clear priority order, validates the language is supported,
+    and injects it into the request context.
+    """
+
+    async def dispatch(self, request: Request, call_next):
+        """
+        Process the request and determine the language.
+        
+        Args:
+            request: The incoming request
+            call_next: The next middleware/handler in the chain
+            
+        Returns:
+            Response with Content-Language header added
+        """
+        # Determine the language for this request
+        language = await self._determine_language(request)
+        
+        # Validate language is supported
+        from app.core.config import settings
+        if language not in settings.I18N_SUPPORTED_LANGUAGES:
+            logger.warning(
+                f"Unsupported language '{language}' requested, "
+                f"falling back to default: {settings.I18N_DEFAULT_LANGUAGE}"
+            )
+            language = settings.I18N_DEFAULT_LANGUAGE
+        
+        # Inject language into request state
+        request.state.language = language
+        
+        # Also set in context variable for exception handling
+        from app.i18n.exceptions import set_current_locale
+        set_current_locale(language)
+        
+        logger.debug(f"Request language set to: {language}")
+        
+        # Process the request
+        response = await call_next(request)
+        
+        # Add Content-Language header to response
+        response.headers["Content-Language"] = language
+        
+        return response
+
+    async def _determine_language(self, request: Request) -> str:
+        """
+        Determine the language to use based on priority order.
+        
+        Priority:
+        1. Query parameter (?lang=en)
+        2. Accept-Language HTTP header
+        3. User language preference (from database)
+        4. Tenant default language
+        5. System default language
+        
+        Args:
+            request: The incoming request
+            
+        Returns:
+            Language code (e.g., "zh", "en")
+        """
+        from app.core.config import settings
+        
+        # 1. Check query parameter (?lang=en)
+        if "lang" in request.query_params:
+            lang = request.query_params["lang"].strip().lower()
+            if lang:
+                logger.debug(f"Language from query parameter: {lang}")
+                return lang
+        
+        # 2. Check Accept-Language HTTP header
+        if "Accept-Language" in request.headers:
+            lang = self._parse_accept_language(
+                request.headers["Accept-Language"]
+            )
+            if lang:
+                logger.debug(f"Language from Accept-Language header: {lang}")
+                return lang
+        
+        # 3. Check user language preference (requires authentication)
+        # Note: This assumes user is already loaded into request.state by auth middleware
+        if hasattr(request.state, "user") and request.state.user:
+            user = request.state.user
+            if hasattr(user, "preferred_language") and user.preferred_language:
+                logger.debug(
+                    f"Language from user preference: {user.preferred_language}"
+                )
+                return user.preferred_language
+        
+        # 4. Check tenant default language
+        # Note: This assumes tenant is already loaded into request.state
+        if hasattr(request.state, "tenant") and request.state.tenant:
+            tenant = request.state.tenant
+            if hasattr(tenant, "default_language") and tenant.default_language:
+                logger.debug(
+                    f"Language from tenant default: {tenant.default_language}"
+                )
+                return tenant.default_language
+        
+        # 5. Fall back to system default language
+        logger.debug(
+            f"Using system default language: {settings.I18N_DEFAULT_LANGUAGE}"
+        )
+        return settings.I18N_DEFAULT_LANGUAGE
+
+    def _parse_accept_language(self, header: str) -> Optional[str]:
+        """
+        Parse the Accept-Language HTTP header.
+        
+        The Accept-Language header format:
+        Accept-Language: zh-CN,zh;q=0.9,en;q=0.8,en-US;q=0.7
+        
+        This method:
+        1. Parses all language codes and their quality values
+        2. Extracts the base language code (zh-CN -> zh)
+        3. Sorts by quality value (higher first)
+        4. Returns the first supported language
+        
+        Args:
+            header: Accept-Language header value
+            
+        Returns:
+            Language code if found and supported, None otherwise
+            
+        Examples:
+            _parse_accept_language("zh-CN,zh;q=0.9,en;q=0.8")
+            # => "zh" (if zh is supported)
+            
+            _parse_accept_language("en-US,en;q=0.9")
+            # => "en" (if en is supported)
+        """
+        from app.core.config import settings
+        
+        if not header:
+            return None
+        
+        # Parse language preferences with quality values
+        languages = []
+        
+        for item in header.split(","):
+            item = item.strip()
+            if not item:
+                continue
+            
+            # Split language code and quality value
+            parts = item.split(";")
+            lang_code = parts[0].strip()
+            
+            # Extract base language code (zh-CN -> zh, en-US -> en)
+            base_lang = lang_code.split("-")[0].lower()
+            
+            # Extract quality value (default: 1.0)
+            quality = 1.0
+            if len(parts) > 1:
+                # Look for q=0.9 pattern
+                q_match = re.search(r"q=([\d.]+)", parts[1])
+                if q_match:
+                    try:
+                        quality = float(q_match.group(1))
+                    except ValueError:
+                        quality = 1.0
+            
+            languages.append((base_lang, quality))
+        
+        # Sort by quality value (descending)
+        languages.sort(key=lambda x: x[1], reverse=True)
+        
+        # Return the first supported language
+        for lang_code, _ in languages:
+            if lang_code in settings.I18N_SUPPORTED_LANGUAGES:
+                return lang_code
+        
+        return None

api/app/i18n/serializers.py

@@ -0,0 +1,219 @@
+"""
+国际化响应序列化器
+
+提供基础的 I18nResponseMixin 类，用于为 API 响应添加国际化字段。
+"""
+
+from typing import Any, Dict, List, Union
+from pydantic import BaseModel
+
+
+class I18nResponseMixin:
+    """国际化响应混入类
+    
+    为响应数据添加国际化字段，特别是为枚举值添加 _display 后缀的翻译字段。
+    
+    使用方法：
+        1. 继承此类
+        2. 实现 _get_enum_fields() 方法定义需要翻译的枚举字段
+        3. 调用 serialize_with_i18n() 方法序列化数据
+    
+    示例：
+        class WorkspaceSerializer(I18nResponseMixin):
+            def _get_enum_fields(self) -> Dict[str, str]:
+                return {
+                    "role": "workspace_role",
+                    "status": "workspace_status"
+                }
+            
+            def serialize(self, workspace: Workspace, locale: str = "zh") -> Dict:
+                data = {
+                    "id": str(workspace.id),
+                    "name": workspace.name,
+                    "role": workspace.role,
+                    "status": workspace.status
+                }
+                return self.serialize_with_i18n(data, locale)
+    """
+    
+    def serialize_with_i18n(
+        self, 
+        data: Any, 
+        locale: str = "zh"
+    ) -> Union[Dict, List[Dict], Any]:
+        """序列化数据并添加国际化字段
+        
+        Args:
+            data: 要序列化的数据（字典、列表或 Pydantic 模型）
+            locale: 语言代码
+            
+        Returns:
+            序列化后的数据，包含国际化字段
+        """
+        # 如果是 Pydantic 模型，转换为字典
+        if isinstance(data, BaseModel):
+            data = data.model_dump()
+        
+        # 处理不同类型的数据
+        if isinstance(data, dict):
+            return self._serialize_dict(data, locale)
+        elif isinstance(data, list):
+            return [self._serialize_dict(item, locale) if isinstance(item, dict) else item for item in data]
+        else:
+            return data
+    
+    def _serialize_dict(self, data: Dict, locale: str) -> Dict:
+        """序列化字典并添加 _display 字段
+        
+        Args:
+            data: 字典数据
+            locale: 语言代码
+            
+        Returns:
+            添加了 _display 字段的字典
+        """
+        from app.i18n.service import translation_service
+        
+        result = data.copy()
+        
+        # 获取需要翻译的枚举字段
+        enum_fields = self._get_enum_fields()
+        
+        # 为每个枚举字段添加 _display 字段
+        for field, enum_type in enum_fields.items():
+            if field in result and result[field] is not None:
+                value = result[field]
+                # 翻译枚举值
+                display_value = translation_service.translate_enum(
+                    enum_type=enum_type,
+                    value=str(value),
+                    locale=locale
+                )
+                # 添加 _display 字段
+                result[f"{field}_display"] = display_value
+        
+        return result
+    
+    def _get_enum_fields(self) -> Dict[str, str]:
+        """获取需要翻译的枚举字段
+        
+        子类必须实现此方法，返回字段名到枚举类型的映射。
+        
+        Returns:
+            字段名到枚举类型的映射
+            例如: {"role": "workspace_role", "status": "workspace_status"}
+        """
+        return {}
+
+
+class WorkspaceSerializer(I18nResponseMixin):
+    """工作空间序列化器
+    
+    为工作空间响应添加国际化字段。
+    """
+    
+    def _get_enum_fields(self) -> Dict[str, str]:
+        """定义工作空间的枚举字段"""
+        return {
+            "role": "workspace_role",
+            "status": "workspace_status"
+        }
+    
+    def serialize(self, workspace_data: Union[Dict, BaseModel], locale: str = "zh") -> Dict:
+        """序列化工作空间数据
+        
+        Args:
+            workspace_data: 工作空间数据（字典或 Pydantic 模型）
+            locale: 语言代码
+            
+        Returns:
+            序列化后的工作空间数据，包含国际化字段
+        """
+        return self.serialize_with_i18n(workspace_data, locale)
+    
+    def serialize_list(self, workspaces: List[Union[Dict, BaseModel]], locale: str = "zh") -> List[Dict]:
+        """序列化工作空间列表
+        
+        Args:
+            workspaces: 工作空间列表
+            locale: 语言代码
+            
+        Returns:
+            序列化后的工作空间列表
+        """
+        return [self.serialize(ws, locale) for ws in workspaces]
+
+
+class WorkspaceMemberSerializer(I18nResponseMixin):
+    """工作空间成员序列化器
+    
+    为工作空间成员响应添加国际化字段。
+    """
+    
+    def _get_enum_fields(self) -> Dict[str, str]:
+        """定义工作空间成员的枚举字段"""
+        return {
+            "role": "workspace_role"
+        }
+    
+    def serialize(self, member_data: Union[Dict, BaseModel], locale: str = "zh") -> Dict:
+        """序列化工作空间成员数据
+        
+        Args:
+            member_data: 成员数据（字典或 Pydantic 模型）
+            locale: 语言代码
+            
+        Returns:
+            序列化后的成员数据，包含国际化字段
+        """
+        return self.serialize_with_i18n(member_data, locale)
+    
+    def serialize_list(self, members: List[Union[Dict, BaseModel]], locale: str = "zh") -> List[Dict]:
+        """序列化工作空间成员列表
+        
+        Args:
+            members: 成员列表
+            locale: 语言代码
+            
+        Returns:
+            序列化后的成员列表
+        """
+        return [self.serialize(member, locale) for member in members]
+
+
+class WorkspaceInviteSerializer(I18nResponseMixin):
+    """工作空间邀请序列化器
+    
+    为工作空间邀请响应添加国际化字段。
+    """
+    
+    def _get_enum_fields(self) -> Dict[str, str]:
+        """定义工作空间邀请的枚举字段"""
+        return {
+            "status": "invite_status",
+            "role": "workspace_role"
+        }
+    
+    def serialize(self, invite_data: Union[Dict, BaseModel], locale: str = "zh") -> Dict:
+        """序列化工作空间邀请数据
+        
+        Args:
+            invite_data: 邀请数据（字典或 Pydantic 模型）
+            locale: 语言代码
+            
+        Returns:
+            序列化后的邀请数据，包含国际化字段
+        """
+        return self.serialize_with_i18n(invite_data, locale)
+    
+    def serialize_list(self, invites: List[Union[Dict, BaseModel]], locale: str = "zh") -> List[Dict]:
+        """序列化工作空间邀请列表
+        
+        Args:
+            invites: 邀请列表
+            locale: 语言代码
+            
+        Returns:
+            序列化后的邀请列表
+        """
+        return [self.serialize(invite, locale) for invite in invites]

api/app/i18n/service.py

@@ -0,0 +1,370 @@
+"""
+Translation service for i18n system.
+
+This module provides the core translation functionality including:
+- Translation lookup with fallback mechanism
+- Parameterized message support
+- Enum value translation
+- Memory caching for performance
+- Performance monitoring and metrics
+"""
+
+import logging
+from functools import lru_cache
+from typing import Any, Dict, Optional
+
+from app.i18n.loader import TranslationLoader
+from app.i18n.cache import TranslationCache
+from app.i18n.metrics import get_metrics, monitor_performance, track_missing_translation, track_translation_request
+from app.i18n.logger import get_translation_logger
+
+logger = logging.getLogger(__name__)
+
+
+class TranslationService:
+    """
+    Translation service that provides:
+    - Fast translation lookup with memory cache
+    - Parameterized message support ({param} syntax)
+    - Fallback mechanism (current locale → default locale → key)
+    - Enum value translation
+    - Deep merge of multi-directory translations
+    """
+
+    def __init__(self, locales_dirs: Optional[list] = None):
+        """
+        Initialize the translation service.
+
+        Args:
+            locales_dirs: List of directories containing translation files.
+                         If None, will auto-detect from settings.
+        """
+        from app.core.config import settings
+
+        self.loader = TranslationLoader(locales_dirs)
+        self.default_locale = settings.I18N_DEFAULT_LANGUAGE
+        self.fallback_locale = settings.I18N_FALLBACK_LANGUAGE
+        self.log_missing = settings.I18N_LOG_MISSING_TRANSLATIONS
+        self.enable_cache = settings.I18N_ENABLE_TRANSLATION_CACHE
+
+        # Initialize advanced cache with LRU
+        lru_cache_size = getattr(settings, 'I18N_LRU_CACHE_SIZE', 1000)
+        self.cache = TranslationCache(
+            max_lru_size=lru_cache_size,
+            enable_lazy_load=False  # Load all at startup for now
+        )
+
+        # Load all translations into cache
+        self._load_all_locales()
+
+        # Initialize metrics
+        self.metrics = get_metrics()
+        
+        # Initialize translation logger
+        self.translation_logger = get_translation_logger()
+
+        logger.info(
+            f"TranslationService initialized with default locale: {self.default_locale}, "
+            f"LRU cache size: {lru_cache_size}"
+        )
+
+    def _load_all_locales(self):
+        """Load all available locales into memory cache."""
+        available_locales = self.loader.get_available_locales()
+        logger.info(f"Loading translations for locales: {available_locales}")
+
+        for locale in available_locales:
+            locale_data = self.loader.load_locale(locale)
+            self.cache.set_locale_data(locale, locale_data)
+
+        logger.info(f"Loaded {len(available_locales)} locales into cache")
+
+    @monitor_performance("translate")
+    def translate(
+        self,
+        key: str,
+        locale: Optional[str] = None,
+        **params
+    ) -> str:
+        """
+        Translate a key to the target locale.
+
+        Supports:
+        - Dot-separated keys (e.g., "common.success.created")
+        - Parameterized messages (e.g., "Hello {name}")
+        - Fallback mechanism
+
+        Args:
+            key: Translation key (format: "namespace.key.subkey")
+            locale: Target locale (defaults to default locale)
+            **params: Parameters for parameterized messages
+
+        Returns:
+            Translated string, or the key itself if translation not found
+
+        Examples:
+            translate("common.success.created", "zh")
+            # => "创建成功"
+
+            translate("common.validation.required", "zh", field="名称")
+            # => "名称不能为空"
+        """
+        if locale is None:
+            locale = self.default_locale
+
+        # Parse key (namespace.key.subkey)
+        parts = key.split(".", 1)
+        if len(parts) < 2:
+            if self.log_missing:
+                logger.warning(f"Invalid translation key format: {key}")
+            return key
+
+        namespace = parts[0]
+        key_path = parts[1].split(".")
+
+        # Track request
+        track_translation_request(locale, namespace)
+
+        # Get translation from cache
+        translation = self.cache.get_translation(locale, namespace, key_path)
+
+        # Fallback to default locale if not found
+        if translation is None and locale != self.fallback_locale:
+            translation = self.cache.get_translation(
+                self.fallback_locale, namespace, key_path
+            )
+
+        # If still not found, return the key itself
+        if translation is None:
+            if self.log_missing:
+                logger.warning(
+                    f"Missing translation: {key} (locale: {locale})"
+                )
+                track_missing_translation(key, locale)
+                
+                # Log to translation logger with context
+                self.translation_logger.log_missing_translation(
+                    key=key,
+                    locale=locale,
+                    context={"namespace": namespace}
+                )
+            return key
+
+        # Apply parameters if provided
+        if params:
+            try:
+                translation = translation.format(**params)
+            except KeyError as e:
+                error_msg = f"Missing parameter in translation '{key}': {e}"
+                logger.error(error_msg)
+                self.translation_logger.log_translation_error(
+                    error_type="parameter_missing",
+                    message=error_msg,
+                    key=key,
+                    locale=locale,
+                    context={"params": list(params.keys())}
+                )
+            except Exception as e:
+                error_msg = f"Error formatting translation '{key}': {e}"
+                logger.error(error_msg)
+                self.translation_logger.log_translation_error(
+                    error_type="format_error",
+                    message=error_msg,
+                    key=key,
+                    locale=locale
+                )
+
+        return translation
+
+    def _get_translation(
+        self,
+        locale: str,
+        namespace: str,
+        key_path: list
+    ) -> Optional[str]:
+        """
+        Get translation from cache (deprecated, use cache.get_translation).
+
+        Args:
+            locale: Locale code
+            namespace: Translation namespace
+            key_path: List of nested keys
+
+        Returns:
+            Translation string or None if not found
+        """
+        return self.cache.get_translation(locale, namespace, key_path)
+
+    @monitor_performance("translate_enum")
+    def translate_enum(
+        self,
+        enum_type: str,
+        value: str,
+        locale: Optional[str] = None
+    ) -> str:
+        """
+        Translate an enum value.
+
+        Args:
+            enum_type: Enum type name (e.g., "workspace_role")
+            value: Enum value (e.g., "manager")
+            locale: Target locale
+
+        Returns:
+            Translated enum display name
+
+        Examples:
+            translate_enum("workspace_role", "manager", "zh")
+            # => "管理员"
+
+            translate_enum("invite_status", "pending", "en")
+            # => "Pending"
+        """
+        key = f"enums.{enum_type}.{value}"
+        return self.translate(key, locale)
+
+    def has_translation(self, key: str, locale: str) -> bool:
+        """
+        Check if a translation exists for the given key and locale.
+
+        Args:
+            key: Translation key
+            locale: Locale code
+
+        Returns:
+            True if translation exists, False otherwise
+        """
+        parts = key.split(".", 1)
+        if len(parts) < 2:
+            return False
+
+        namespace = parts[0]
+        key_path = parts[1].split(".")
+
+        translation = self.cache.get_translation(locale, namespace, key_path)
+        return translation is not None
+
+    def reload(self, locale: Optional[str] = None):
+        """
+        Reload translation files.
+
+        Args:
+            locale: Specific locale to reload. If None, reloads all locales.
+        """
+        logger.info(f"Reloading translations for locale: {locale or 'all'}")
+
+        if locale:
+            locale_data = self.loader.load_locale(locale)
+            self.cache.set_locale_data(locale, locale_data)
+            # Clear LRU cache for this locale
+            self.cache.clear_locale(locale)
+        else:
+            self._load_all_locales()
+            # Clear all LRU cache
+            self.cache.clear_lru()
+
+        logger.info("Translation reload completed")
+
+    def get_available_locales(self) -> list:
+        """
+        Get list of all available locales.
+
+        Returns:
+            List of locale codes
+        """
+        return self.cache.get_loaded_locales()
+    
+    def get_cache_stats(self) -> Dict[str, Any]:
+        """
+        Get cache statistics.
+        
+        Returns:
+            Dictionary with cache statistics
+        """
+        return self.cache.get_stats()
+    
+    def get_metrics_summary(self) -> Dict[str, Any]:
+        """
+        Get metrics summary.
+        
+        Returns:
+            Dictionary with metrics summary
+        """
+        return self.metrics.get_summary()
+    
+    def get_memory_usage(self) -> Dict[str, Any]:
+        """
+        Get memory usage information.
+        
+        Returns:
+            Dictionary with memory usage information
+        """
+        return self.cache.get_memory_usage()
+
+    def get_loaded_dirs(self) -> list:
+        """
+        Get list of loaded translation directories.
+
+        Returns:
+            List of directory paths
+        """
+        return self.loader.locales_dirs
+
+
+# Global singleton instance
+_translation_service: Optional[TranslationService] = None
+
+
+def get_translation_service() -> TranslationService:
+    """
+    Get the global translation service instance.
+
+    Returns:
+        TranslationService singleton
+    """
+    global _translation_service
+    if _translation_service is None:
+        _translation_service = TranslationService()
+    return _translation_service
+
+
+# Convenience functions for easy access
+def t(key: str, locale: Optional[str] = None, **params) -> str:
+    """
+    Translate a key (convenience function).
+
+    Args:
+        key: Translation key
+        locale: Target locale (optional, uses default if not provided)
+        **params: Parameters for parameterized messages
+
+    Returns:
+        Translated string
+
+    Examples:
+        t("common.success.created")
+        t("common.validation.required", field="名称")
+        t("workspace.member_count", count=5)
+    """
+    service = get_translation_service()
+    return service.translate(key, locale, **params)
+
+
+def t_enum(enum_type: str, value: str, locale: Optional[str] = None) -> str:
+    """
+    Translate an enum value (convenience function).
+
+    Args:
+        enum_type: Enum type name
+        value: Enum value
+        locale: Target locale
+
+    Returns:
+        Translated enum display name
+
+    Examples:
+        t_enum("workspace_role", "manager")
+        t_enum("invite_status", "pending", "en")
+    """
+    service = get_translation_service()
+    return service.translate_enum(enum_type, value, locale)