At Ask Ubuntu everything is in English. Are there any German language websites for Ubuntu?
Ubuntu comes with many different languages including all variants of German. This also includes manuals and helpfiles for most applications included. Different to this providing different locales to the main Ubuntu website would make it very hard to maintain.
Still there is an "official" German Ubuntu forum where you can get help on all topics:
People there also maintain a tremendously helpful Wiki for many topics and applications. Asking questions or participating in discussions requires registration which is free of charge.
Besides https://ubuntuusers.de/, which Takkat mentioned, there are German translations of the official documentation:
The pages will be displayed in the preferred language specified by your browser, so to make Firefox show the docs in German, select Edit -> Preferences -> Content -> Languages and make German be the first language in that list.