Is that really the case? So it means they can meet in, say, St. John building as a different conggregation (not attending the same service as the Slavic-based St. John)?
I'm a member of a Latin Mass community that holds our Masses in a church that has regular vernacular Masses at other times.
When I was teaching in Turkey, I attended Mass at a French church, which was used by Syrians to hold their Masses earlier on Sunday morning.
It can be done, and makes sense if the congregation, the Bishop, and the host church can get together on it.