Yes, that is the case. The whole topic can be written natively in 20 languages and will be served in German to a German reader, if the supported languages include German.
Discourse will not provide recommendations on which model you should use, so you should choose a model which supports translating to the languages of your choise.
Mentioned in docs is also the ability to customize the persona that includes the prompt and model. 
I don’t really understand what you mean here, can you elaborate or share what this question is?
Not sure if this is what you mean, but CDCK will unlikely provide any other paid services, however - A customer on our hosting may set up this feature with the CDCK-hosted models but there are language limits based on which tier they are on.