"From German, after the Karst, a limestone plateau near Trieste, Slovenia". Non quite. The word may have entered the English language through German, but Trieste in neither in Germany, nor in Slovenia. It is in Italy, and the limestone plateau near Trieste has an Italian name, i.e. "Carso". Apart from a short period of time, when it was under Austrian rule, and an even shorter period of time (after World War II) when it was Slovenian, the region has always been Italian (or at least Neo-Latin) from a linguistic point of view. So, unless we want to imagine a pre-Roman etimology for Mount Carso and the Carso area, Karst should be taken as of Italian etimology.