The 'Kitsai' (also 'Kichai') language is an extinct
Caddoan language. It was spoken in
Oklahoma and became extinct in the 1930s. It is documented in the still mostly-unpublished fieldnotes of anthropologist
Alexander Lesser. It is thought to be most closely related to
Wichita.
References
http://www.native-languages.org/kitsai.htm
http://www.texasbeyondhistory.net/tejas/fundamentals/languages.html
http://www.ethnologue.com/14/show_language.asp?code=KII