Spirits are high in the class I’m crashing on an April night at a community center in Castroville, a small town 25 miles west of San Antonio. About fifty of us, including the mayor, sit in folding chairs while the language teacher, a man from Alsace, a region in northeast France that passed back and forth between that country and Germany over the centuries, leads us in a song praising a schnitzelbank. That’s the Alsatian word for “workbench,” a fitting muse for this crowd of industrious Texas Alsatians, most of whom trace their lineage back to Castroville’s founding, in 1844. We practice two more songs: “S’Elsass Unser Landel!” (“Alsace Our Land!”) and “Texas, Our Texas.” The class’s organizer, Mark Haby, tells us, “Remember, we will sing…