Inside the glass-walled studio, three talk-radio hosts are having a wonderful time. They are sitting around a table, headphones on, relaxed and garrulous; their stream of conversation, much of it in French, is a patter of news, political invective, call-in chat, history quizzes. They groove to the D.J.’s pop selections — Reel 2 Real’s “I Like to Move It” (move it) — or they sing themselves. It’s 1994, in Rwanda. “Be happy, friends!” they sing, in between calling for their neighbors’ deaths. “God is always just!” The director Milo Rau’s chilling “Hate Radio,” from 2011, which began performances on Thursday...