Dashboard language?

I would like to build the site in German (since it takes a long time and you can’t find anything), although (I’m not one of the authors) all authors write in English. I can’t find any way to change the dashboard to German.

I downloaded (installed) another theme for free, but it still shows the old one. In WP everyone knows where to find the templates, but not here. I’m starting to despair, as this is the second attempt to understand a completely counter-intuitive system. Who can help?

The dashboard is not part of the theme, and there’s no translation of it available. Sorry!