LocaleMiddleware creates wrong redirects when combined with script prefix

[Tilman Koschnick]

If a Django instance is mounted with a prefix, e.g. with

WSGIScriptAlias /some_prefix /path/to/wsgi.py

and i18n_patterns are used, the generated redirect urls have the language prefix before the script prefix, e.g.:

http://host/some_prefix/some_path/ -> http://host/en/some_prefix/some_path/

Correct would be to put the language prefix between script prefix and the rest of the path:

http://host/some_prefix/some_path/ -> http://host/some_prefix/en/some_path/

The attached patch fixes this, pulling the required bits from request.META.

[Bas Peschier]

This is a duplicate of #21579