Classification
Tlingit is currently classified as a distinct and separate branch of the Na-Dené family of North American languages, with its closest relative being Eyak. Edward Sapir (1915) argued for its inclusion in the Na-Dené family, a claim which was subsequently debated by Franz Boas (1917), P.E. Goddard (1920), and many other prominent linguists of the time.
Studies in the late 20th century by Heinz-Jürgen Pinnow (1962, 1968, 1970, int. al.) and Michael Krauss (1964, 1965, 1969, int. al.) showed a strong connection to Eyak and hence to the Athabaskan languages. This relationship is now widely accepted.
Sapir initially proposed a connection between Tlingit and Haida, but the debate over Na-Dené gradually excluded Haida from the discussion. Haida is now considered an isolate with some borrowing through long proximity with Tlingit. The Haida linguist John Enrico has recently presented (2004) new arguments which have reopened the debate.
Read more about this topic: Tlingit Language