Language in Ukraine: Why Russian vs. Ukrainian divides so deeply

It wasn’t fighting Russian-speaking separatists in Ukraine that spurred Roman Nabozhniak to stop speaking Russian. It was being misidentified on vacation as a Russian.

Mr. Nabozniak was one of thousands of Ukrainian volunteers who fought rebels in the Moscow-leaning Donbass region, who rose against the central government in Kyiv in 2014 citing in part its “violation” of their right to speak Russian. Backed by Russian weaponry and volunteers, the separatists forcibly carved out two “people’s republics,” where anyone speaking Ukrainian could be thrown in what rights groups and survivors call “concentration camps.”

Mr. Nabozniak and his comrades in arms, on the other hand, were linguistically mixed. Some volunteers came from western, Ukrainian-speaking regions. But others were from Kyiv or, like Mr. Nabozniak, from the central city