A Chinese-American family goes to China to visit the grandmother who is dying, but no one has told her the truth of her condition, in this tender comedy of grief and family. The premise of The Farewell, the second feature from writer/director Lulu Wang, is fairly simple. Billi, a young Chinese American woman, is told by her parents that her grandmother in China, whom she calls Nai Nai, has been diagnosed with a fatal cancer and has only a few months to live. The catch is that no one has told Nai Nai this fact. It is the social custom…