NYC is the world's capital of endangered languages.

Alex Carp, The Endangered Languages of New York, NYTimes, Feb. 22, 2024.

Most people think of endangered languages as far-flung or exotic, the opposite of cosmopolitan. “You go to some distant mountain or island, and you collect stories,” the linguist Ross Perlin says, describing a typical view of how such languages are studied. But of the 700 or so speakers of Seke, most of whom can be found in a cluster of villages in Nepal, more than 150 have lived in or around two apartment buildings in Brooklyn. Bishnupriya Manipuri, a minority language of Bangladesh and India, has become a minority language of Queens.

All told, there are more endangered languages in and around New York City than have ever existed anywhere else, says Perlin, who has spent 11 years trying to document them. And because most of the world’s languages are on a path to disappear within the next century, there will likely never be this many in any single place again.

Perlin's book: Language City: The Fight to Preserve Endangered Mother Tongues in New York (2024).

With Daniel Kaufman, also a linguist, Perlin directs the Endangered Language Alliance, in Manhattan. When E.L.A. was founded, in 2010, Perlin lived in the Chinese Himalayas, where he studied Trung, a language with no standard writing system, dictionary or codified grammar. (His work helped establish all three.) He spent most of his time in the valley where the largest group of remaining speakers lived; the only road in or out was impassable in winter. [...]

Since their project began, Perlin and Kaufman have located speakers of more than 700 languages. Of those languages, at least 150 are listed as under significant threat in at least one of three major databases for the field. Perlin and Kaufman consider that figure to be conservative, and Perlin estimates that more than half of the languages they documented may be endangered.

There's more at the link.