Saruul is studying to be an engineer when she agrees to take the last job her cosmopolitan but still relatively conservative Mongolian parents would ever imagine their daughter doing: selling intimacy aids in a basement-level sex shop. Technically, Saruul’s just filling in for a shy friend at school who trusts her to be discreet, but this temporary gig has a subtle yet life-changing impact on the title character, who looks like she could be 14 years old at first, but blossoms into a more self-aware young woman over “The Sales Girl’s” slightly overlong running time.

The top prize winner of the New York Asian Film Festival, veteran director Sengedorj Janchivdorj’s umpteenth feature takes a frank, sex-positive approach to the titillating world in which it’s set. But that doesn’t make this an erotic film. Instead, “The Sales Girl” focuses mostly on the unlikely friendship between Saruul (Bayartsetseg...