Open the file General.opt that is inside the settings folder with a text editor like notepad.
Then change to this, 3 is german
Language = 3
ThirdLanguage = 3
Save and close the file and run the game, should be in german now.
I do not use german, so not sure everything was translated.
It is the same procedure for any Ageod game as long as has been translated.
You can check the localstrings files in the same folder for the localizations in several languages.