I agree with Lederhosen. If you already have an license, like you have, your good to go!
Any ICAO-license will allow you to convert straight to a German UL-license. In Germany it is called SPL-F (Sportpiloten Lizenz -beiblatt F)
I have done the conversion with my FAA-PPL and it took me 1 day at the flight school. All I had to do was getting a medical and 3written exams
(Human Performance, Air Law and Pyrotechnic . Since a german reg Ultraleicht is equipped with a ballistic recovery system (parachute) you also have to do Pyrotechnics because of the solid-fuel rocket system .
US-PPL, Umschreibung US-PPL in UL-Lizenz (SPL)
Happy landings!