diff --git a/django/middleware/locale.py b/django/middleware/locale.py
index f693e4d242..be0e549495 100644
--- a/django/middleware/locale.py
+++ b/django/middleware/locale.py
@@ -17,6 +17,14 @@ class LocaleMiddleware(object):
     is available, of course).
     """
 
+    def __init__(self):
+        self._supported_languages = dict(settings.LANGUAGES)
+        self._is_language_prefix_patterns_used = False
+        for url_pattern in get_resolver(None).url_patterns:
+            if isinstance(url_pattern, LocaleRegexURLResolver):
+                self._is_language_prefix_patterns_used = True
+                break
+
     def process_request(self, request):
         check_path = self.is_language_prefix_patterns_used()
         language = translation.get_language_from_request(
@@ -26,9 +34,11 @@ class LocaleMiddleware(object):
 
     def process_response(self, request, response):
         language = translation.get_language()
-        if (response.status_code == 404 and
-                not translation.get_language_from_path(request.path_info)
-                    and self.is_language_prefix_patterns_used()):
+        language_from_path = translation.get_language_from_path(
+                request.path_info, supported=self._supported_languages
+        )
+        if (response.status_code == 404 and not language_from_path
+                and self.is_language_prefix_patterns_used()):
             urlconf = getattr(request, 'urlconf', None)
             language_path = '/%s%s' % (language, request.path_info)
             path_valid = is_valid_path(language_path, urlconf)
@@ -42,8 +52,9 @@ class LocaleMiddleware(object):
                     request.get_host(), language, request.get_full_path())
                 return HttpResponseRedirect(language_url)
         translation.deactivate()
-
-        patch_vary_headers(response, ('Accept-Language',))
+        if not (self.is_language_prefix_patterns_used()
+                and language_from_path):
+            patch_vary_headers(response, ('Accept-Language',))
         if 'Content-Language' not in response:
             response['Content-Language'] = language
         return response
@@ -53,7 +64,4 @@ class LocaleMiddleware(object):
         Returns `True` if the `LocaleRegexURLResolver` is used
         at root level of the urlpatterns, else it returns `False`.
         """
-        for url_pattern in get_resolver(None).url_patterns:
-            if isinstance(url_pattern, LocaleRegexURLResolver):
-                return True
-        return False
+        return self._is_language_prefix_patterns_used
diff --git a/django/utils/translation/__init__.py b/django/utils/translation/__init__.py
index 292e4db869..ace87fab4b 100644
--- a/django/utils/translation/__init__.py
+++ b/django/utils/translation/__init__.py
@@ -165,8 +165,8 @@ def to_locale(language):
 def get_language_from_request(request, check_path=False):
     return _trans.get_language_from_request(request, check_path)
 
-def get_language_from_path(path):
-    return _trans.get_language_from_path(path)
+def get_language_from_path(path, supported=None):
+    return _trans.get_language_from_path(path, supported=supported)
 
 def templatize(src, origin=None):
     return _trans.templatize(src, origin)
diff --git a/django/utils/translation/trans_null.py b/django/utils/translation/trans_null.py
index 5c51468204..7ef07793a4 100644
--- a/django/utils/translation/trans_null.py
+++ b/django/utils/translation/trans_null.py
@@ -58,6 +58,6 @@ def to_locale(language):
 def get_language_from_request(request, check_path=False):
     return settings.LANGUAGE_CODE
 
-def get_language_from_path(request):
+def get_language_from_path(request, supported=None):
     return None
 
diff --git a/tests/regressiontests/i18n/patterns/tests.py b/tests/regressiontests/i18n/patterns/tests.py
index 639e03f288..0a785ab1d6 100644
--- a/tests/regressiontests/i18n/patterns/tests.py
+++ b/tests/regressiontests/i18n/patterns/tests.py
@@ -172,6 +172,26 @@ class URLRedirectTests(URLTestCaseBase):
         self.assertEqual(response.status_code, 200)
 
 
+class URLVaryAcceptLanguageTests(URLTestCaseBase):
+    """
+    Tests that 'Accept-Language' is not added to the Vary header when using
+    prefixed URLs. 
+    """
+    def test_no_prefix_response(self):
+        response = self.client.get('/not-prefixed/')
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.get('Vary'), 'Accept-Language')
+
+    def test_en_redirect(self):
+        response = self.client.get('/account/register/', HTTP_ACCEPT_LANGUAGE='en')
+        self.assertRedirects(response, '/en/account/register/')
+        self.assertFalse(response.get('Vary'))
+
+        response = self.client.get(response['location'])
+        self.assertEqual(response.status_code, 200)
+        self.assertFalse(response.get('Vary'))
+
+
 class URLRedirectWithoutTrailingSlashTests(URLTestCaseBase):
     """
     Tests the redirect when the requested URL doesn't end with a slash
diff --git a/tests/regressiontests/i18n/tests.py b/tests/regressiontests/i18n/tests.py
index ad184d8da3..aaa9b12c3b 100644
--- a/tests/regressiontests/i18n/tests.py
+++ b/tests/regressiontests/i18n/tests.py
@@ -48,7 +48,8 @@ from .models import Company, TestModel
 from .patterns.tests import (URLRedirectWithoutTrailingSlashTests,
     URLTranslationTests, URLDisabledTests, URLTagTests, URLTestCaseBase,
     URLRedirectWithoutTrailingSlashSettingTests, URLNamespaceTests,
-    URLPrefixTests, URLResponseTests, URLRedirectTests, PathUnusedTests)
+    URLPrefixTests, URLResponseTests, URLRedirectTests, PathUnusedTests,
+    URLVaryAcceptLanguageTests)
 
 
 here = os.path.dirname(os.path.abspath(upath(__file__)))