fix i18n

src/capport/api/lang.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import re
 import typing
 import quart
+import os.path
 
 from .app import app
 
@@ -49,14 +50,15 @@ def detect_language():
     g = quart.g
     r = quart.request
     s = quart.session
-    lang = r.args.get('setlang')
-    if lang:
-        lang = lang.strip().lower()
+    if 'setlang' in r.args:
+        lang = r.args.get('setlang').strip().lower()
         if lang and _VALID_LANGUAGE_NAMES.match(lang):
-            s = quart.session
             s['lang'] = lang
             g.langs = [lang]
             return
+        else:
+            # reset language
+            s.pop('lang')
     lang = s.get('lang')
     if lang:
         lang = lang.strip().lower()
@@ -65,3 +67,15 @@ def detect_language():
             return
     acc_lang = ','.join(r.headers.get_all('Accept-Language'))
     g.langs = parse_accept_language(acc_lang)
+
+
+async def render_i18n_template(template, /, **kwargs) -> str:
+    langs: typing.List[str] = quart.g.langs
+    if not langs:
+        return await quart.render_template(template, **kwargs)
+    names = [
+        os.path.join('i18n', lang, template)
+        for lang in langs
+    ]
+    names.append(template)
+    return await quart.render_template(names, **kwargs)