[4.2.x] Fixed #34455 -- Restored i18n_patterns() respect of prefix_default_language argument when fallback language is used.

Regression in 94e7f471c4edef845a4fe5e3160132997b4cca81.

Thanks Oussama Jarrousse for the report.

Backport of 3b4728310a7a64f8fcc548163b0aa5f98a5c78f5 from main

2 files changed, 4 insertions, 2 deletions

diff --git a/django/urls/resolvers.py b/django/urls/resolvers.py
index 9a22b0d87d..e5c6dfdea7 100644
--- a/django/urls/resolvers.py
+++ b/django/urls/resolvers.py
@@ -23,7 +23,7 @@ from django.utils.datastructures import MultiValueDict
 from django.utils.functional import cached_property
 from django.utils.http import RFC3986_SUBDELIMS, escape_leading_slashes
 from django.utils.regex_helper import _lazy_re_compile, normalize
-from django.utils.translation import get_language
+from django.utils.translation import get_language, get_supported_language_variant
 
 from .converters import get_converter
 from .exceptions import NoReverseMatch, Resolver404
@@ -351,7 +351,8 @@ class LocalePrefixPattern:
     @property
     def language_prefix(self):
         language_code = get_language() or settings.LANGUAGE_CODE
-        if language_code == settings.LANGUAGE_CODE and not self.prefix_default_language:
+        default_language = get_supported_language_variant(settings.LANGUAGE_CODE)
+        if language_code == default_language and not self.prefix_default_language:
             return ""
         else:
             return "%s/" % language_code
diff --git a/django/utils/translation/__init__.py b/django/utils/translation/__init__.py
index 0b3f78e486..69820a2fc4 100644
--- a/django/utils/translation/__init__.py
+++ b/django/utils/translation/__init__.py
@@ -17,6 +17,7 @@ __all__ = [
     "get_language_from_request",
     "get_language_info",
     "get_language_bidi",
+    "get_supported_language_variant",
     "check_for_language",
     "to_language",
     "to_locale",