Yes, in the admin settings you can change the locale of the UI, and 99% of our text has German counterparts (you can see language coverage on Crowdin Enterprise)
There are a variety of examples on our website, Discourse customers | Discourse - Civilized Discussion
This can vary by feature, their carousel is custom, but much of the other changes were accomplished using CSS alone. We also have a variety of customizations in the Customization > Theme component category here on Meta that can make things like banners, additional nav links, and featured posts easier to implement.