what is the language spoken by the last nation you mentioned?
The Arapaho language.
Arapaho
The Arapaho language is currently spoken in two different dialects, and it is considered to be a member of the Algonquian language family. 
what were the terms of the treaty of fort laramie why did it fall One of the terms was that  it established the Great Sioux Reservation including ownership of the Black Hills, and set aside additional lands as "unceded Indian territory" in areas of South Dakota, Wyoming, and Nebraska, and possibly Montana. It failed as neither parties fully honored the terms. who was this treaty signed by? The United States and the Oglala, Miniconjou, and Brulé bands of Lakota people, Yanktonai Dakota and Arapaho Nation.
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Arapaho [SEP] Language
The Arapaho language is currently spoken in two different dialects, and it is considered to be a member of the Algonquian language family. The number of fluent speakers of Northern Arapaho dwindles at 250, most living on the Wind River Reservation in Wyoming, while the number of Southern Arapaho speakers is even more scarce, only a handful of people speak it, all advanced in age. According to Cowell & Moss's 2008 study of the Arapaho language, the Northern Arapaho have made a great effort to maintain the language through establishing the Language and Culture Commission. By producing audio and visual materials, they have provided ways for younger generations to learn the language.