The Ukrainian language is like Gaelic in Ireland, people claim to speak it, but most do speak Russian.
Russian supremacists have a long history of Russifying the lands they control. Language is obvious a key part of that and historically local languages were banned. There are already reports of Ukrainian book burnings in occupied Ukraine, etc.
Lots more here:
https://en.wikipedia.org/wiki/Chronology_of_Ukrainian_language_suppression