In less than two months, the indie film Dear You has become an unlikely mass hit. Shot in the Teochew language from the Chaoshan region of southern China’s Guangdong province, the movie follows a man uncovering his family’s past by tracing remittance letters sent home from Thailand. As he pieces together his grandfather’s life story, the movie also explores Chinese migration to the region and the diaspora’s struggle to preserve its heritage. In one scene, an elderly schoolmaster risks arrest in...