Use system locale for default request language

Remove en_US as the default language when no header is provided, and use
None instead. Upon translation None will be defaulted to system locale
as it was before API translation changes.

fixes bug 1214476

Change-Id: Ic33c94c29993ceb944d7c22d2e754cb938db7503

nova/api/openstack/wsgi.py

@@ -179,10 +179,15 @@ def get_content_type(self):
         return content_type
 
     def best_match_language(self):
-        """Determine language for returned response."""
+        """Determine the best available language for the request.
+
+        :returns: the best language match or None if the 'Accept-Language'
+                  header was not available in the request.
+        """
+        if not self.accept_language:
+            return None
         return self.accept_language.best_match(
-                gettextutils.get_available_languages('nova'),
-                default_match='en_US')
+                gettextutils.get_available_languages('nova'))
 
 
 class ActionDispatcher(object):

nova/tests/api/openstack/test_faults.py

@@ -60,7 +60,7 @@ def raiser(*args, **kwargs):
 
         self.assertIn("I've been translated!", unicode(response.body))
         mock_get_localized.assert_any_call(
-                u'Should be translated.', 'en_US')
+                u'Should be translated.', None)
 
 
 class TestFaults(test.NoDBTestCase):

nova/tests/api/openstack/test_wsgi.py

@@ -143,7 +143,16 @@ def test_none_found(self):
         request = wsgi.Request.blank('/')
         accepted = 'nb-no'
         request.headers = {'Accept-Language': accepted}
-        self.assertEqual(request.best_match_language(), 'en_US')
+        self.assertIs(request.best_match_language(), None)
+
+    def test_no_lang_header(self):
+        self.stubs.Set(gettextutils, 'get_available_languages',
+                       fakes.fake_get_available_languages)
+
+        request = wsgi.Request.blank('/')
+        accepted = ''
+        request.headers = {'Accept-Language': accepted}
+        self.assertIs(request.best_match_language(), None)
 
 
 class ActionDispatcherTest(test.NoDBTestCase):