Hello the decription says the game support german audio and text.
But there isn't. The installer shows only english and the galaxy load english too.

1. You forgot to mention which game you are talking about.

2.1 Anyway, the games all support multiple languages. I checked all 4 installers and except Arkham Knight all show multiple languages to chose from. You need to click on "options" and change the "game language". I don't know why the option isn't there for Arkham Knight, but it really dosen't matter anyway, since:

2.2 Arkham Knight has a file called LanguageSelector.exe in the same directory as the game's main executable.

It's a bit inconsistent, sure. But it does the trick.