Russian troops in Ukraine started wearing Ukrainian uniforms to disorient the population and sneak deep into the territory. In response, the Ukrainian army switched entirely to speaking Ukrainian.
In Ukraine, everybody is bilingual. People who don’t speak fluent Ukrainian understand it completely. But Russians don’t understand Ukrainian at all.
All of the rumors about the supposed persecution of Russian-speakers in Ukraine are pure rubbish. Ukrainian TV, for instance, is completely bilingual. Somebody speaks in Ukrainian, another person responds in Russian, and everybody is happy. In public spaces, the languages are used interchangeably. Official documents are all in Ukrainian but that’s always been the case. Back in 1998, I ran into trouble in Canada when I was applying to college and the Canadian bureaucrats kept demanding that I send them documents in Russian. I obviously didn’t have such documents because Russian wasn’t our official language.