GoogleTranslate offers translation to/from several of China's indigenous languages, the latest being Uyghur.
Others are Kazakh, Korean, Kyrgyz and Mongolian.
Turkmen and Tatar have also just joined the club -- and Turkish had long been available -- so Google Translate is doing a decent job of adding Turkic languages.
But in terms of written scripts used by a large number of PRC citizens, one stands out as missing on this list: Tibetan. It appears that its inclusion is underway, but I don't have any details.