According to illustrations and literature, the crwth appears to have been played widely across Europe, not just Wales. It's mentioned in Chaucer and players were designated by the surname Crowther in England and MacWhirter in Scotland. The crwth was probably most common in Finland and the Swedish-speaking coastal bit of Estonia where there is a substantial body of surviving music for the instrument. The "modern" Welsh crwth (which isn't really much like the traditional ancient lyre-like one) dates only to the late C16 or early C17 and was pretty much wiped out by two factors: the rise of rampant Welsh protestantism and the growth in popularity of that Italian import, the violin, by the end of C18. Revival crwths are built mainly by West country English luthiers. Ah, cultural diversity . . .