I recently created a new tag: mathematical-german.
Other than English, the main languages in which mathematics is published are French, German and Russian. We have a tag mathematical-french already. Thus, why not have a tag for German, too? One could post questions on the German Language SE, but there are Germans on Mathematics SE who can arguably provide more accurate translations.
If I read a translation of a mathematical term in German Language SE, how can I trust the answer? In Mathematics SE, I can click on someone's profile. If this someone has a lot of points in, say, real analysis, then I can trust that someone's translation of a German term used in real analysis. Especially if that someone has a German name.