They don’t know the words. They don’t speak Russian. Still, millions of TikTok users keep hitting replay on a 1938 Soviet song about a girl on a riverbank. “Katyusha” arrived on the platform not as a dusty historical artifact but as a thumping, shareable soundtrack, chopped, bass-boosted, and repackaged for short-form video. You may have heard it under gym montages, drifting-car edits, and cinematic clips of men in fatigues. In a few bars it reconnects strangers across languages to something that feels at once mournful, heroic, and strangely triumphant. The question isn’t just what the song is, but why a...