Australia has topped a list of "hot spots" for the extinction of Indigenous languages.
The list was put together by linguists from the Enduring Voices project, which seeks to document and revitalise languages slipping toward oblivion.
David Harrison of Swarthmore College in Pennsylvania, the project's co-director, says there are 6,992 recognised distinct languages worldwide.
He says on average, one language vanishes every two weeks, often as its last elderly speakers perish.
The project, backed by National Geographic magazine, named a region of northern Australia including parts of Queensland, the Northern Territory and Western Australia as the place where local languages are most threatened.
The linguists say Aboriginal Australia harbours some of the most endangered languages, with 153 different ones spoken in this region.
A region of central South America covering Ecuador, Colombia, Peru, Brazil and Bolivia was second on the list of "hot spots", with Indigenous languages being overcome by Spanish, Portuguese or other indigenous languages.
The linguists says Bolivia has twice the language diversity of the nations of Europe combined, but many of the smaller tongues are being smothered by Spanish or other languages.
Placing third and fifth on the list were regions of North America where the languages of native peoples are imperilled - an area including British Columbia in Canada and the US states of Washington and Oregon, and an area covering the US states of Oklahoma, Texas and New Mexico.
Eastern Siberia, also with endangered native languages, was the number 4 "hot spot".
"There are quite a few languages, dozens if not hundreds, that are down to one, two or three speakers, or maybe even they've lost their last fluent speakers but have a few 'semi-speakers' who have a passive knowledge of the language," Mr Harrison said.
"We're going to lose an immense storehouse of knowledge," Mr Harrison added, noting for example that valuable information accumulated over centuries about various living species exists in languages of native peoples.
Many languages have no written form, meaning that they are lost forever when their last speaker dies, Mr Harrison said.
"Languages often trickle out of existence rather than sort of abruptly disappearing," said Gregory Anderson, co-director of the Enduring Voices project and director of the non-profit Living Tongues Institute for Endangered Languages.
Over the years, some languages have been deliberately exterminated by colonisers or aggressors taking over territory or waging genocide, the linguists said.
Children now often decide a language's fate, Mr Harrison said, by abandoning an ancestral tongue for another language they see as more widely used, for example, on television or in school.
The linguists with the Enduring Voices project have been travelling to interview the last speakers of certain languages.
"We'll start with a basic 100- or 200-word list. And then we'll go over each word with them again to make sure that we're transcribing it correctly, and try to repeat it to them," Mr Anderson said.
"And usually they'll burst out laughing at that point because we have hideously mispronounced it ... or make some word that sounds obscene to them. ... I did that in Australia, I'm afraid," Mr Anderson added.