I'm a bit puzzled by the "at" instead of "of" - none of my English-to-English law dictionaries or my English-German legal dictionaries state this term in this form (and I've never heard it put this way practicing or studying law).

I'm assuming, though, that it is the same as a court of law, which used to be the term used to distinguish these courts from proceedings in equity. These days, it is a rather formal way of referring to any court, especially a trial court.

In any case, I would leave the US-term unchanged and add the German translation in brackets.