In Canada, there are four Siouan languages, all belonging to the Dakotan sub-branch of the family, they are Dakota (Santee-Sisseton), Lakota (Teton), Nakoda (Assiniboine), and Nakoda (Stoney). Nakoda (Stoney) is only in Alberta, the rest are also to be found in the United States. A fifth Dakotan language: Dakota (Yankton-Yanktonai) has speakers only in the U.S.” cited from Language Geek at http://www.languagegeek.com/siouan/siouan.html
Formerly, the Dakota language was only a spoken language. However, today it can be written. “The first alphabet for Sioux, known as Riggs, was devised by the missionaries Samuel and Gideon Pond, Stephen Return Riggs and Dr Thomas S. Williamson in 1834. They based their spelling system on the Santee dialect (Dakota) and used it to translate biblical texts into that dialect. The Dakota translation of the bible was well known and used among the Dakota and Lakota.” Cited from Omniglot at https://www.omniglot.com/writing/sioux.htm