Fixed #26271 -- Fixed i18n_patterns resolution when no language is active

Thanks Marten Kenbeek for the report.

django/urls/resolvers.py

@@ -11,6 +11,7 @@ import functools
 import re
 from importlib import import_module
 
+from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.utils import lru_cache, six
 from django.utils.datastructures import MultiValueDict
@@ -388,7 +389,7 @@ class LocaleRegexURLResolver(RegexURLResolver):
 
     @property
     def regex(self):
-        language_code = get_language()
+        language_code = get_language() or settings.LANGUAGE_CODE
         if language_code not in self._regex_dict:
             regex_compiled = re.compile('^%s/' % language_code, re.UNICODE)
             self._regex_dict[language_code] = regex_compiled

tests/i18n/patterns/tests.py

@@ -2,6 +2,7 @@ from __future__ import unicode_literals
 
 import os
 
+from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.http import HttpResponsePermanentRedirect
 from django.middleware.locale import LocaleMiddleware
@@ -75,6 +76,8 @@ class URLPrefixTests(URLTestCaseBase):
             self.assertEqual(reverse('prefixed'), '/en/prefixed/')
         with translation.override('nl'):
             self.assertEqual(reverse('prefixed'), '/nl/prefixed/')
+        with translation.override(None):
+            self.assertEqual(reverse('prefixed'), '/%s/prefixed/' % settings.LANGUAGE_CODE)
 
     @override_settings(ROOT_URLCONF='i18n.patterns.urls.wrong')
     def test_invalid_prefix_use(self):