Hello :)
I'm sorry that my question seems to be kind of stupid, but I really can't find where to change the language in this game. According to GOG Galaxy I can do that but I really don't know how to. Am I blind or is it hidden somewhere in the game options?

If you're using GoG Galaxy, there should be an option called Language Setup in the "More"-menu, of your Darksiders page. Alternatively, go to the install directory of Darksiders2. Therein should be a file called "language_setup.exe". Start the .exe to bring up the language selection dialog.

Thanks! I should have checked the game folder.