Can I play a game from France on my German Xbox One?

I've just seen a French version of Rock Band 4 on Ebay and wanted to ask if that would work on my Xbox One S.

That's a good question, as Germany is well known for censoring a lot in movies, games co.
As I know, but Rock Band 4 is already available here.

Would the language be French or would that be German?

Is different, as it is, but from France will be spoken on any case France.
Btw. They have no obligation to add the German language there.

So I had bought the game "Guitar Hero Live" for the One S on Amazon and that came in a box with French writing on it. Came me somehow funny before but has worked for me, maybe that works well

Yes works, with luck, the German language is with, otherwise English is also there