Fixed #16332 -- Added language template tag that switches the activate...

Fixed #16332 -- Added language template tag that switches the activate language for the enclosed template section, e.g. to allow translation of URLs as added in r16405. Many thanks to Florian Apolloner and Orne Brocaar.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16501 bcc190cf-cafb-0310-a4f2-bffc1f526a37