Hey there @Skipii90, and welcome to the forums.
This is the English-language forum for the game, but we have a German language forum available Here!
That being said, I can provide you with a few things to try and get your NPC audio working.
First, Verify your game files through Ubisoft Connect.
After that, open the in-game sound settings menu and make sure that the language and volume for every type of audio is set correctly. Take a screenshot of these settings for me while you have that menu open!
Finally, run through the basic audio troubleshooting steps Here.
If you are able to reply to this thread in English feel free to reply here with the results of these steps, otherwise you can open another thread on the German discussions board!