I have been keeping tabs on this question, and I am confident that I could answer the question.
The problem is, OPs major issue is that they are using a copy of the game that was censored, for release in Germany. If they were accessing the regular game, they would be able to fix their problem.
I know how to redirect to the original game, as I had to do something similar when Left 4 Dead 2 was censored here in Australia.
The solution should fix their problems, but would also circumnavigate the censorship restrictions on the game.
Is such an answer permitted, or should I just leave it? The answer would involve editing two of the game files associating it with steam, so that instead of launching the censored version through steam, the user would instead launch the regular uncensored version, along with the language support they are requesting.