Nag Ashwin’s Telugu-language mythological sci-fi epic Kalki 2898 AD is like many modern South Indian blockbusters, in that it draws roars of approval from crowds in theaters for major cameos. That might not sound too different from your average Marvel movie, but while Hollywood’s cameos usually depend on familiar characters showing up from other films, the cheers for “special appearances” during hits in languages like Tamil and Telugu are usually for...