Background: Edward Sapir (; January 26, 1884 - February 4, 1939) was an American anthropologist-linguist, who is widely considered to be one of the most important figures in the early development of the discipline of linguistics. Sapir was born in German Pomerania; his parents emigrated to United States of America when he was a child. He studied Germanic linguistics at Columbia, where he came under the influence of Franz Boas who inspired him to work on Native American languages.
Context: Sapir's special focus among American languages was in the Athabaskan languages, a family which especially fascinated him. In a private letter, he wrote: "Dene is probably the son-of-a-bitchiest language in America to actually know...most fascinating of all languages ever invented." Sapir also studied the languages and cultures of Wishram Chinook, Navajo, Nootka, Colorado River Numic, Takelma, and Yana. His research on Southern Paiute, in collaboration with consultant Tony Tillohash, led to a 1933 article which would become influential in the characterization of the phoneme.  Although noted for his work on American linguistics, Sapir wrote prolifically in linguistics in general. His book Language provides everything from a grammar-typological classification of languages (with examples ranging from Chinese to Nootka) to speculation on the phenomenon of language drift, and the arbitrariness of associations between language, race, and culture. Sapir was also a pioneer in Yiddish studies (his first language) in the United States (cf. Notes on Judeo-German phonology, 1915).  Sapir was active in the international auxiliary language movement. In his paper "The Function of an International Auxiliary Language", he argued for the benefits of a regular grammar and advocated a critical focus on the fundamentals of language, unbiased by the idiosyncrasies of national languages, in the choice of an international auxiliary language.  He was the first Research Director of the International Auxiliary Language Association (IALA), which presented the Interlingua conference in 1951. He directed the Association from 1930 to 1931, and was a member of its Consultative Counsel for Linguistic Research from 1927 to 1938. Sapir consulted with Alice Vanderbilt Morris to develop the research program of IALA.
Question: what languages did he study?. Whats the answer?
Sapir's special focus among American languages was in the Athabaskan languages,