diff --git a/django/middleware/locale.py b/django/middleware/locale.py
index dd154e1280..b5e4949378 100644
--- a/django/middleware/locale.py
+++ b/django/middleware/locale.py
@@ -19,6 +19,7 @@ class LocaleMiddleware(object):
 
     def process_response(self, request, response):
         patch_vary_headers(response, ('Accept-Language',))
-        response['Content-Language'] = translation.get_language()
+        if 'Content-Language' not in response:
+            response['Content-Language'] = translation.get_language()
         translation.deactivate()
         return response