It is probably very unlikely that you are looking for the German equivalent of Radio Operator's certificates like the Long Range Certificate (LRC) for world-wide operation on VHF, HF and satellites, or the Short Range Certificate (SRC) for VHF traffic on coastal waters, or the UBI for European inland waterways.
But just in case - I am training Radio Operators since more than 20 years now. Since about five years I am trainer for radio certificates in one of Hannover's yachting schools: the Segelschule Altwarmbüchener See. If you need more information then please contact me or the school directly.