It doesn't seem like a pleasant, bilateral collaboration since Russian developers do not seem pleased about the Euro-Office initiative.[0]

[0]: https://github.com/ONLYOFFICE#%EF%B8%8F-legal-note

Yes, but they can't do anything about it anyway. The FSF resolution on this matter, though, essentially means that they might just as well pull Euro-Office patches into OnlyOffice. So in the end, the product will be formed by combined effort.