This is the reality in most big (and older) companies, where choice of language, OS, etc., are dictated by who’s available, what they know and “how it’s always been done”, rather than by other considerations that only the technically minded may worry a lot more about.
You didn’t state which uncommon language the experienced programmers like. Since Python libraries are usually written in other languages (like C, or some even in Rust in recent times), you could probably consider giving them the task of writing the low level algorithmic/library work if this is suitable for the product design and if these experienced programmers like a language that can be easily used to write Python libraries. The team members who know Python can work on all the high level stuff.
I don’t think there’s an ideal solution for your situation, more so when we don’t have a lot of details here.