Thirty men costumed in the white blouses, short fitted jackets and knee breeches of ancient Europe arrayed themselves across the edge of the food court at the 1990 Festival International de Louisiane. They raised the shiny black shafts of reed instruments that looked like oboes and bagpipes.

A swirling, droning sound enveloped the crowd; their drummers beat a lively tattoo. The group was called, we found, Kevrenn Alre. Regardless, we had a question: if this was a fest that presents French-...