Redirects broken: double url encoding, language ignored

Problem/Motivation

Redirects do not work. Issues:
* Uris are encoded twice
* Language code is not respected
* Complex logic, but no tests

Steps to reproduce

German site, transliterate files and check if redirects for files do work. Can be specifically interesting for PDF documents.

Proposed resolution

See MR. Fixed the duplicated encoding and added tests for redirect creation.

Also successful transliterated files are optionally logged.