feat: add backend i18n response support

app/factory.py

@@ -1,10 +1,35 @@
-from fastapi import FastAPI
+from typing import Awaitable, Callable
+
+from fastapi import FastAPI, HTTPException, Request, Response
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import JSONResponse
 
 from app.core.config import settings
+from app.helper.locale import LocaleHelper
 from app.startup.lifecycle import lifespan
 
 
+async def localized_http_exception_handler(
+        _request: Request,
+        exc: HTTPException,
+) -> JSONResponse:
+    """
+    为 HTTPException 响应补充多语言错误详情。
+
+    :param _request: 当前 HTTP 请求
+    :param exc: FastAPI HTTP 异常
+    :return: 带 detail_i18n 的 JSON 错误响应
+    """
+    content = {"detail": exc.detail}
+    if isinstance(exc.detail, str):
+        content["detail_i18n"] = LocaleHelper.translate_text(exc.detail)
+    return JSONResponse(
+        status_code=exc.status_code,
+        content=content,
+        headers=exc.headers,
+    )
+
+
 def create_app() -> FastAPI:
     """
     创建并配置 FastAPI 应用实例。
@@ -15,6 +40,8 @@ def create_app() -> FastAPI:
         lifespan=lifespan
     )
 
+    _app.add_exception_handler(HTTPException, localized_http_exception_handler)
+
     # 配置 CORS 中间件
     _app.add_middleware(
         CORSMiddleware,  # noqa
@@ -24,6 +51,22 @@ def create_app() -> FastAPI:
         allow_headers=["*"],
     )
 
+    @_app.middleware("http")
+    async def locale_context_middleware(
+            request: Request,
+            call_next: Callable[[Request], Awaitable[Response]],
+    ) -> Response:
+        """
+        为每个请求设置后端多语言上下文。
+        """
+        token = LocaleHelper.set_current_locale(
+            LocaleHelper.get_locale_from_request(request)
+        )
+        try:
+            return await call_next(request)
+        finally:
+            LocaleHelper.reset_current_locale(token)
+
     return _app