Two years ago, a team of linguists plunged into the remote hill country of northeastern India to study little-known languages, many of them unwritten and in danger of falling out of use.

On average, every two weeks one of the world’s recorded 7,000 languages becomes extinct, and the expedition was seeking to document and help preserve the endangered ones in these isolated villages.

At a rushing mountain river, the linguists crossed on a bamboo raft and entered the tiny village of Kichang. They expected to hear the people speaking Aka, a fairly common tongue in that district. Instead, they heard a language, the linguists said, that sounded as different from Aka as English does from Japanese.

After further investigation, leaders of the research announced last week the discovery of a “hidden” language, known locally as Koro, completely new to the world outside these rural communities. While the number of spoken languages continues to decline, at least one new one has been added to the inventory, though Koro too is on the brink of extinction.

“We noticed it instantly” as a distinct and unfamiliar language, said Gregory Anderson, director of the Living Tongues Institute for Endangered Languages in Salem, Ore.

Anderson and K. David Harrison, a linguist at Swarthmore College, were leaders of the expedition, part of the Enduring Voices Project of the National Geographic Society. Another member of the group was Ganash Murmu, a linguist at Ranchi University in India. A scientific paper will be published by the journal Indian Linguistics.

When the three researchers reached Kichang, they went door to door asking people to speak their native tongue — not a strenuous undertaking in a village of only four bamboo houses set on stilts. The people live by raising pigs and growing oranges, rice and barley. They share a subsistence economy and a culture with others in the region who speak Aka, or Miji, another somewhat common language.

On the veranda at one house, the linguists heard a young woman named Kachim telling her life story in Koro. She was sold as a child bride, was unhappy in her adopted village and had to overcome hardships before eventually making peace with her new life.

Listening, the researchers at first suspected Koro to be a dialect of Aka, but its words, syntax and sounds were entirely different. Few words in Koro were the same as in Aka: Mountain in Aka is “phu,” but “nggo” in Koro; pig in Aka is “vo,” but in Koro “lele.” The two languages share only 9 percent of their vocabulary.

The linguists recorded Kachim’s narrative in Koro, and an Indian TV crew had her repeat it in Hindi. This not only enabled the researchers to understand her story and her language, but called attention to the cultural pressures threatening the survival of such languages, up against national languages dominant in schools, commerce and mass media.

In “The Last Speakers: The Quest to Save the World’s Most Endangered Languages,” published last month by National Geographic Books, Harrison noted that Koro speakers “are thoroughly mixed in with other local peoples and number perhaps no more than 800.”

Moreover, linguists are not sure how Koro has survived this long as a viable language. Harrison wrote: “The Koro do not dominate a single village or even an extended family. This leads to curious speech patterns not commonly found in a stable state elsewhere.”

By contrast, the Aka people number about 10,000 living in close relations with Koro speakers in a district of the state of Arunachal Pradesh, where at least 120 languages are spoken. Anderson said the coexistence of separate languages between two integrated groups that do not acknowledge an ethnic difference between them is highly unusual.

As Harrison and Anderson expanded their research, comparing Koro with several hundred languages, they determined that it belonged to the Tibeto-Burman language family, which includes 400 tongues related to widely used Tibetan and Burmese. But Koro had never been recognized in any surveys of the approximately 150 languages spoken in India.

The effort to identify “hot spots of threatened languages,” the linguists said, is critical in making decisions to preserve and enlarge the use of such tongues, which are repositories of a people’s history and culture.

In the case of Koro speakers, Harrison wrote in his book, “even though they seem to be gradually giving up their language, it remains the most powerful trait that identifies them as a distinct people.”

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