Moving into the final three posts of this series now; and for X we have the Xibe language.
I mentioned the Xibe (or, Xibo) language briefly in my earlier post about the Manchu language; but it certainly warrants its own post too. It is also a Tungusic language, still spoken by approximately 30,000 people in the northwest of China. It is considered to be closely related to Manchu – whether it is a dialect of Manchu or not is a matter of debate – but it is clear that it has survived far better than the Manchu language.
The Xibe people in the northwest of China descend from a garrison that was stationed there from around the 18th century. It is not immediately clear why the Xibe language has survived longer than Manchu, but it could be due to the fact that most of the Xibe population live in a contained area (as opposed to the scattered Manchus), or there could be a lower degree of contact with the dominant Han. However, in recent years, increased contact means that there are more chances for assimilation and, subsequently, loss of language and culture, in the future.
Wikipedia: Xibe language
Omniglot: Xibe language, alphabet and pronunciation
Sohu: Story Almost Over for Xibe Language
Travel China Guide: Chinese Xibe People
China.org.cn: Ethnic Groups – The Xibe Ethnic Minority