Fixed #11161 -- Added plural forms to all supported languages. Fixed other errors in the translation files that prevented them to pass the msgfmt check in preparation for the move to Transifex. Refs #14735, too.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14771 bcc190cf-cafb-0310-a4f2-bffc1f526a37