Fix #11890: Append slash at locale root URL

lib/l10n_utils/__init__.py

@@ -166,7 +166,10 @@ def render(request, template, context=None, ftl_files=None, activation_files=Non
 
         # Does that path's locale match the request's locale?
         if locale in translations:
-            if locale != request.path.lstrip("/").partition("/")[0]:
+            # Redirect to the locale if:
+            # - The URL is the root path but is missing the trailing slash OR
+            # - The locale isn't in current prefix in the URL.
+            if request.path == f"/{locale}" or locale != request.path.lstrip("/").partition("/")[0]:
                 return redirect_to_locale(request, locale)
         else:
             return redirect_to_best_locale(request, translations)

lib/l10n_utils/tests/test_base.py

@@ -62,6 +62,8 @@ class TestRender(TestCase):
         self._test("/firefox/new/", template, "", "", 404, active_locales=locales)
 
         # Test that a locale+path and no accept language header returns 200 as long as the locales are supported.
+        self._test("/en-US", template, "", "", 302, "/en-US/", active_locales=locales)
+        self._test("/en-US/", template, "", "", 200, active_locales=locales)
         self._test("/en-US/firefox/new/", template, "", "", 200, active_locales=locales)
         self._test("/en-GB/firefox/new/", template, "", "", 200, active_locales=locales)
         self._test("/fr/firefox/new/", template, "", "", 200, active_locales=locales)