In “Schindler’s List,” most of the actors spoke English, using accents to indicate their characters’ origins. In “Son of Saul,” the cast struggles to communicate in a mish-mosh of languages, as Jews of different nationalities were thrown together in Auschwitz-Birkenau. Stories about the Holocaust — so vital in trying to reconcile the horrors of the past century — must at some point take a philosophical stand on how to deal with how their characters express themselves.