With the exception of one band, ALL of the federally-recognized Siouan tribes use the word “Sioux” in their official name. Likewise, virtually all of the Assiniboine/Ojibwe tribes actually use the word “Chippewa” in their official name. Almost all tribes are known by a name applied by other tribes or by Europeans. Most tribes in their own language call themselves by a word that means something like “The people,” e.g. Dine for the Navaho, Aniyunwiya for the Cherokee. Few tribes are known to others by those ‘personal’ names. If you ask me what I am, I will tell you I’m Cherokee. I think it makes the most sense to use the English name that the modern tribes have chosen to use when we are writing in English.