This is not a strange thing in “revived” countries.
In the current autonomous Spanish regions of the Basque country and Catalunya, the Basque and Catalan languages are official, and required in the schools. And thats in spite of them having large minorities of 20th century economic immigrants from elsewhere in Spain - who spoke and still speak Spanish of course. The result is an almost universal bilingualism.
I, a native Spanish speaker, live in Bilbao and often go to Barcelona. This all has very little political friction there.
The cause of this trouble in Ukraine is obviously irredentism deliberately created by the Russian government.
You will find such cases everywhere in Europe. France forced French on Nice. Britain English on Wales. The Baltic states on their own large minorities of Russian speakers.