Aliased trans_null.to_locale() to trans_real.to_locale().

The implementations have unintentionally diverged.

django/utils/translation/trans_null.py

@@ -4,6 +4,8 @@
 
 from django.conf import settings
 
+from .trans_real import to_locale as trans_real_to_locale
+
 
 def gettext(message):
     return message
@@ -52,12 +54,7 @@ def check_for_language(x):
     return True
 
 
-def to_locale(language):
-    p = language.find('-')
-    if p >= 0:
-        return language[:p].lower() + '_' + language[p + 1:].upper()
-    else:
-        return language.lower()
+to_locale = trans_real_to_locale
 
 
 def get_language_from_request(request, check_path=False):

tests/i18n/tests.py

@@ -286,6 +286,7 @@ class TranslationTests(SimpleTestCase):
         for lang, locale in tests:
             with self.subTest(lang=lang):
                 self.assertEqual(to_locale(lang), locale)
+                self.assertEqual(trans_null.to_locale(lang), locale)
 
     def test_to_language(self):
         self.assertEqual(trans_real.to_language('en_US'), 'en-us')