Ensure locale names are cleared entirely when needed

`lru_cache.cache_clear` only clears the cache in the current thread.

wagtail/admin/tests/test_templatetags.py

@@ -312,7 +312,8 @@ class TestComponentTag(SimpleTestCase):
         ("fr", "French"),
         ("ro", "Romanian"),
         ("ru", "Russian"),
-    ]
+    ],
+    CACHES={"default": {"BACKEND": "django.core.cache.backends.locmem.LocMemCache"}},
 )
 class TestInternationalisationTags(TestCase):
     def setUp(self):

wagtail/coreutils.py

@@ -11,6 +11,7 @@ from anyascii import anyascii
 from django.apps import apps
 from django.conf import settings
 from django.conf.locale import LANG_INFO
+from django.core.cache import cache
 from django.core.cache.utils import make_template_fragment_key
 from django.core.exceptions import ImproperlyConfigured, SuspiciousOperation
 from django.core.signals import setting_changed
@@ -334,17 +335,21 @@ def get_supported_content_language_variant(lang_code, strict=False):
     raise LookupError(lang_code)
 
 
-@functools.lru_cache
 def get_locales_display_names() -> dict:
     """
     Cache of the locale id -> locale display name mapping
     """
     from wagtail.models import Locale  # inlined to avoid circular imports
 
-    locales_map = {
-        locale.pk: locale.get_display_name() for locale in Locale.objects.all()
-    }
-    return locales_map
+    cached_map = cache.get("wagtail_locales_display_name")
+
+    if cached_map is None:
+        cached_map = {
+            locale.pk: locale.get_display_name() for locale in Locale.objects.all()
+        }
+        cache.set("wagtail_locales_display_name", cached_map)
+
+    return cached_map
 
 
 @receiver(setting_changed)

wagtail/signal_handlers.py

@@ -2,6 +2,7 @@ import logging
 from contextlib import contextmanager
 
 from asgiref.local import Local
+from django.core.cache import cache
 from django.db import transaction
 from django.db.models.signals import (
     post_delete,
@@ -12,7 +13,6 @@ from django.db.models.signals import (
 )
 from modelcluster.fields import ParentalKey
 
-from wagtail.coreutils import get_locales_display_names
 from wagtail.models import Locale, Page, ReferenceIndex, Site
 
 logger = logging.getLogger("wagtail")
@@ -39,7 +39,7 @@ def post_delete_page_log_deletion(sender, instance, **kwargs):
 
 
 def reset_locales_display_names_cache(sender, instance, **kwargs):
-    get_locales_display_names.cache_clear()
+    cache.delete("wagtail_locales_display_name")
 
 
 reference_index_auto_update_disabled = Local()