I agree scenarios with a language barrier can be hot, at least in theory .
But to work, such scenarios would have to be built around the fact that they will be in a language the sub does not understand. It should probably be designed such that the Domme can do her things without depending on compliance from the sub. Otherwise it gets awkward when the Domme gives an order and the sub does nothing or something completely different.

And of course, there must be a way to agree and understand limits upfront.

If it can work, I might be tempted to suggest something like this, if I ever find myself in a language-barrier-challenged situation again. The Domme speaking confidently in a language I don't understand at all might work better than very limited English.
Then again, I will probably rather head for the safety of an English-speaking Mistress.