MTG: What set is Seelenruhe (Tranquility in German) from?
This card is a Revised German Tranquility. For English sets without a set symbol only Alpha and Beta have black borders. But when Magic started out whenever a Core set was printed for the first time in a language it had black borders. The first printing of German Magic cards was Revised Edition, Strangely it seems that German Revised had at least 2 printings, one in black border and one in white.

Reference: Revised German Tranquility on Scryfall