feat(i18n): add English localization with per-user language preference and navbar toggle

app/routers/web.py

@@ -22,6 +22,7 @@ from random import choice
 from string import ascii_letters, digits
 
 from app.models import InviteCode, Postcard, Profile, User
+from app.i18n import t as _t
 
 router = APIRouter(tags=["web"])
 templates = Jinja2Templates(directory=str(Path(__file__).resolve().parent.parent / "templates"))
@@ -66,6 +67,13 @@ def _strftime(dt: datetime, fmt: str) -> str:
 templates.env.filters["strftime"] = _strftime
 
 
+def _translate_filter(key: str, lang: str = "zh") -> str:
+    return _t(key, lang)
+
+
+templates.env.filters["t"] = _translate_filter
+
+
 def _redirect(url: str) -> RedirectResponse:
     return RedirectResponse(url, status_code=303)
 
@@ -353,6 +361,19 @@ def change_password(
     )
 
 
+@router.post("/settings/language")
+def change_language(
+    request: Request,
+    language: str = Form(...),
+    user: User = Depends(get_current_user_web),
+    db: Session = Depends(get_db),
+):
+    if language in ("zh", "en"):
+        user.language = language
+        db.commit()
+    return _redirect(request.headers.get("referer", "/settings"))
+
+
 # ---------- Auth ----------
 
 @router.get("/logout")
@@ -798,4 +819,5 @@ def public_showcase(request: Request, username: str, db: Session = Depends(get_d
     return templates.TemplateResponse("showcase.html", {
         "request": request, "profile_user": user, "mode": user.showcase_mode,
         "profile_groups": profile_groups, "sent_all": sent_all, "received_all": received_all,
+        "lang": user.language,
     })