There’s a bracing image partway through “Amrum,” a new historical drama from the director Fatih Akin, that has the makings of an antifascist meme. It’s the spring of 1945, and word of the Second World War’s impending end has reached the residents of Amrum, an island off the coast of Germany. The general response to this news seems muted; apart from an outspoken potato farmer (Diane Kruger) who looks forward to the conclusion of “Hitler’s damn war,” the islanders know that their rage against the Nazi regime is, like an illegal radio or extra rations, something best kept to themselves....