fix(i18n): honor Accept-Language q-values in locale resolver (#225)

lobby/i18n.py

@@ -39,15 +39,22 @@ def resolve_locale(request: HttpRequest) -> str:
     default_locale, supported_locales = i18n_locale_config()
 
     accept_language = request.META.get("HTTP_ACCEPT_LANGUAGE") or ""
-    for candidate in accept_language.split(","):
+    ranked_candidates: list[tuple[float, int, str]] = []
+    for index, candidate in enumerate(accept_language.split(",")):
         quality = _quality_value(candidate)
         if quality is not None and quality <= 0:
             continue
 
         tag = candidate.split(";", 1)[0]
         normalized = tag.strip().replace("_", "-").split("-", 1)[0].lower()
-        if normalized in supported_locales:
-            return normalized
+        if normalized not in supported_locales:
+            continue
+
+        ranked_candidates.append((quality if quality is not None else 1.0, index, normalized))
+
+    if ranked_candidates:
+        ranked_candidates.sort(key=lambda entry: (-entry[0], entry[1]))
+        return ranked_candidates[0][2]
 
     requested = (get_language_from_request(request) or "").replace("_", "-").split("-", 1)[0].lower()
     if requested in supported_locales:

lobby/tests.py

@@ -1300,7 +1300,7 @@ class I18nResolverTests(TestCase):
         self.assertEqual(response.status_code, 400)
         self.assertEqual(resolve_locale(response.wsgi_request), "en")
 
-    def test_resolve_locale_keeps_q08_languages_eligible_in_accept_language_loop(self):
+    def test_resolve_locale_prefers_highest_quality_supported_language(self):
         response = self.client.post(
             reverse("lobby:join_session"),
             data={"code": "", "nickname": "Luna"},
@@ -1309,7 +1309,7 @@ class I18nResolverTests(TestCase):
         )
 
         self.assertEqual(response.status_code, 400)
-        self.assertEqual(resolve_locale(response.wsgi_request), "da")
+        self.assertEqual(resolve_locale(response.wsgi_request), "en")
 
     def test_resolve_locale_defaults_to_en_when_header_missing(self):
         response = self.client.post(