Another language, Wakhi, from eastern Iran as well as parts of Pakistan, China, Tajikistan and Afghanistan, is believed to be spoken by less than a handful of people in New York, according to the language alliance.

One speaker, Husniya Khujamyorova, 31, who works as a linguist at the organization, is writing children’s books in Wakhi in the hopes of passing down the language, which is spoken by about 40,000 people worldwide. “People like me, they move at an early age from their country,” Ms. Khujamyorova said. “There is not enough material to pass their language to the new generation.”

Even if a language is spoken by only a few people, language experts say it still plays a vital role.

“It’s absolutely invaluable to document, analyze, understand and maintain the linguistic diversity of the planet,” said Ross Perlin, a director of the language alliance and an adjunct professor of linguistics at Columbia University. “But we also see it as a matter of justice — languages are not dying a natural death. They’re disappearing because people have been marginalized and pressured and made to feel bad to speak their language, or they’re swamped by a dominant language.”

“Just like diversity with the environment, language loss represents an immense tragedy for the world,” he added.

As for Seke, which means “golden language,” legend has it that it was passed down from people living in the snowy peaks of the Himalayas who settled in Mustang, a former kingdom whose terrain was formed, so the story goes, from the heart and innards of a demon defeated in battle by a Buddhist monk.

The apartment building in Flatbush where a number of Seke speakers now live is a microcosm of life back home and a bastion of the language.