This may be a start to help answer your question:
<https://www.change.org/p/deutscher-bundestag-%C3%A4nderung-des-fernmeldegeheimnisses?utm_campaign=petition_created&utm_medium=email&utm_source=guides>
From there you will likely have to follow more law documents and/or contact someone at Bundesnetzagentur (BNetzA) and ask why they still have this World War II-era law for no good reason...and don't provide reasonable exclusions for educational activities like listening to ATC.