Most local language schools offer online courses in addition to classroom courses.
You can still find these offers under "Language courses in Potsdam" or "Language courses in Berlin". Under "Language courses on the net" you will find a list of providers who only offer online courses.
German language and short courses in all over Germany can be found here.
University of Potsdam
Welcome Center Potsdam
Am Neuen Palais 10, bldg. 8, room 1.11
Tel.: +49 331 977-1382 | -153052