I had no idea there were entire languages left to discover.   Then again, I had no idea there was a group called the Living Tongues Institute for Endangered Languages either, but exist they both do.  
The linguists, doing a project for National Geographic, thought these people in the northeast corner of India were speaking a dialect of the Aka culture of the Himalayas - but it turns out they have a different vocabulary and linguistic structure.

The language called Koro is so unknown even its speakers, about 1,000 people, didn't know it was distinct.   Linguists say the addition of Koro brings the number of documented languages up to 6,910.   They say the discovery was important because a language "dies" about every two weeks with the loss of its last speakers.

They say the Koro language is a member of the Tibeto-Burman language family, which includes 400 languages such as, you guessed from its name, Tibetan and Burmese.

Living Tongues Institute for Endangered Languages

National Geographic Enduring Voices