set_language with next unset and a urlencoded HTTP_REFERER fails redirection

[Miikka Salminen]

POSTing to set_language when next is not set causes Django to user HTTP_REFERER instead. If the URL in HTTP_REFERER is urlencoded, the resulting redirection will fail.

The bug is caused by the call to translate_url function in set_language. translate_url passes the URL on to reverse, which assumes URLs that are not urlencoding, thus resulting in a double urlencoded URL, which obviously will not work. Non-urlencoded URLs in HTTP_REFERER work correctly.

An easy way to test this is to have a view with a URL with unicode characters in it and use the translation selector widget provided in the i18n docs, but with the redirect_to context variable undefined, which is the way I found the bug.

AFAIK there's no standard about whether the browser should encode the URL in HTTP_REFERER, but most of the new browsers do so anyway. The bug should be easy to fix, thus, by just decoding the string in HTTP_REFERER – if it was encoded, it will now be unencoded, if it was not encoded, it will be unchanged (disregarding a corner case of ambiguous URLs with substrings like %C3%A4 verbatim with browsers that don't encode the URLs). I'll make a pull request within a few days.