Mute Witness (1995) on Netflix

Moscow, 1993. In an old cinema studio building, an American producer is filming a low budget slasher film. The director, Andy Clark (Evan Richards), is working with his girlfriend, Karen Hughes (Fay Ripley), as his assistant, and his girlfriend's sister, Billy Hughes (Marina Zudina), as his FX make-up artist. Billy is a very pretty young blonde girl, but she doesn't have the physical ability to speak, not even to utter the merest sound. But she isn't deaf.