Fixed #26046 -- Fixed a crash with translations and Django-unknown language code

Thanks Jens Lundstrom for the report and Tim Graham for the review.

django/utils/translation/trans_real.py

@@ -117,6 +117,9 @@ class DjangoTranslation(gettext_module.GNUTranslations):
             # default lang should have at least one translation file available.
             raise IOError("No translation files found for default language %s." % settings.LANGUAGE_CODE)
         self._add_fallback()
+        if self._catalog is None:
+            # No catalogs found for this language, set an empty catalog.
+            self._catalog = {}
 
     def __repr__(self):
         return "<DjangoTranslation lang:%s>" % self.__language