As far as I understood german air law & exams & LuftVO etc. You are bound by the laws of the country that you are currently flying in / over.
Being a UK Citizen with a UK licence in a D reg aircraft in Germany should not make a difference. With an international EASA or still a JAR PPL(A), as I understood it, you are allowed to fly european registered aircraft wherever you may find them.
You would be bound by the Luftfahrtgesetze & the LuftVO.
The wording "Entgelt" and "renumeration" match up according to Leo translation. However there is a lot of difference between the meaning / interpretation of the two. I would also go with a translation issue here. It wouldn't be the first time...
And if all else fails I suppose one could find a very good restaurant and let your passengers buy you dinner...
Regards
ITSAB