Fixed #13514 -- Corrected the process of loading multiple javascript translation catalogs. Thanks to jtiai for the report, to Ramiro Morales for working out the test case, and to Ramiro and Jannis for their help on the fix.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13250 bcc190cf-cafb-0310-a4f2-bffc1f526a37