diff --git a/django/core/extensions.py b/django/core/extensions.py
index e9947f0c6e..591e7ad740 100644
--- a/django/core/extensions.py
+++ b/django/core/extensions.py
@@ -37,9 +37,9 @@ class DjangoContext(Context):
         from django.conf import settings
         self['LANGUAGES'] = settings.LANGUAGES
         if hasattr(request, 'LANGUAGE_CODE'):
-            self['LANGUAGE_CODE'] = request.LANGUAGE_CODE
+            self['LANGUAGE_CODE'] = request.LANGUAGE_CODE.replace('_', '-')
         else:
-            self['LANGUAGE_CODE'] = settings.LANGUAGE_CODE
+            self['LANGUAGE_CODE'] = settings.LANGUAGE_CODE.replace('_', '-')
         if DEBUG and request.META.get('REMOTE_ADDR') in INTERNAL_IPS:
             self['debug'] = True
             from django.core import db