It would not be overstating matters to argue that Louis Garrel comes from French thespian royalty. His grandfather was the busy actor Maurice Garrel. His dad has been directing for more than 50 years and, just this year, at the age of 74, won best director at the Berlin Film Festival. Brigitte Sy, his mother, is a tireless actor, director and educator. Garrel was surely destined — doomed? — to a life on the screen. “No, to be honest. In the beginning I was only interested in playing on stage,” he says in lively, fluid English. “My dream, when I...