GOG has games in German and various other languages; you can filter by language on the search page.

Hello and welcome to GOG.com.
There are already many games on GOG that support more than one languages:
Take a look here.

GOG usually tries to get German versions of the games that the sell, and have added German version to many games that didn't have them previously. They can't always provide one, though, because especially for localized versions of old games, the legal and licensing situation is often very messy. It's often unclear who owns the localized content and who is able to provide a valid license that GOG can sell to customers.

If you ask about German games that never had an English version, then the answer is probably "No", though you'd have to contact GOG directly if you want a more reliable answer. But given that the entire store, all advertising, the payment dialog, community activities, and practically everything else is in English, I don't think that adding German-only games is planned, or would be worth the effort.

You can of course add the respective to the wishlist if you like.

Thanks for all your replies.
I asked probably for adventure games because there it is sometimes hard to play in englisch.

BR

Here is a list with all Adventure games that support German.