1. is something that can be explained in a blanket way for each language folder,
I agree, a README for each language directory would be enough.
I guess. 2 probably needs to be done in the code.
Yes, as it is already done, but I agree that the current description should be extended.
Not sure where 3 would go. Maybe a README.
I think that 3 is part of the context and how to run them. So yes, part of the language folder README, or as part of the general README.