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When every known speaker of the language Amurdag gets together, there's still no one to talk to.

Native Australian Charlie Mungulda is the only person alive known to speak that language, one of thousands around the world on the brink of extinction.

From rural Australia to Siberia to Oklahoma, languages that embody the history and traditions of people are dying, researchers said Tuesday.

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While there are an estimated 7,000 languages spoken around the world today, one of them dies out about every two weeks, according to linguistic experts struggling to save at least some of them.

Five hotspots where languages are most endangered were listed Tuesday in a briefing by the Living Tongues Institute for Endangered Languages and the National Geographic Society.

In addition to northern Australia, eastern Siberia and Oklahoma and the U.S. Southwest, many native languages are endangered in South America — Ecuador, Colombia, Peru, Brazil and Bolivia — as well as the area including British Columbia, and the states of Washington and Oregon.

Losing languages means losing knowledge, says K. David Harrison, an assistant professor of linguistics at Swarthmore College.

"When we lose a language, we lose centuries of human thinking about time, seasons, sea creatures, reindeer, edible flowers, mathematics, landscapes, myths, music, the unknown and the everyday."

As many as half of the current languages have never been written down, he estimated.

That means, if the last speaker of many of these vanished tomorrow, the language would be lost because there is no dictionary, no literature, no text of any kind, he said.

Harrison is associate director of the Living Tongues Institute based in Salem, Ore. He and institute director Gregory D.S. Anderson analyzed the top regions for disappearing languages.

Anderson said languages become endangered when a community decides that its language is an impediment. The children may be first to do this, he explained, realizing that other more widely spoken languages are more useful.

The key to getting a language revitalized, he said, is getting a new generation of speakers. He said the institute worked with local communities and tries to help by developing teaching materials and by recording the endangered language.

Harrison said that the 83 most widely spoken languages account for about 80 percent of the world's population while the 3,500 smallest languages account for just 0.2 percent of the world's people. Languages are more endangered than plant and animal species, he said.

The hot spots listed at Tuesday's briefing:

— Northern Australia, 153 languages. The researchers said aboriginal Australia holds some of the world's most endangered languages, in part because aboriginal groups splintered during conflicts with white settlers. Researchers have documented such small language communities as the three known speakers of Magati Ke, the three Yawuru speakers and the lone speaker of Amurdag.

— Central South America including Ecuador, Colombia, Peru, Brazil and Bolivia — 113 languages. The area has extremely high diversity, very little documentation and several immediate threats. Small and socially less-valued indigenous languages are being knocked out by Spanish or more dominant indigenous languages in most of the region, and by Portuguese in Brazil.

— Northwest Pacific Plateau, including British Columbia in Canada and the states of Washington and Oregon in the U.S., 54 languages. Every language in the American part of this hotspot is endangered or moribund, meaning the youngest speaker is over age 60. An extremely endangered language, with just one speaker, is Siletz Dee-ni, the last of 27 languages once spoken on the Siletz reservation in Oregon.

— Eastern Siberian Russia, China, Japan — 23 languages. Government policies in the region have forced speakers of minority languages to use the national and regional languages and, as a result, some have only a few elderly speakers.

— Oklahoma, Texas and New Mexico — 40 languages. Oklahoma has one of the highest densities of indigenous languages in the United States. A moribund language of the area is Yuchi, which may be unrelated to any other language in the world. As of 2005, only five elderly members of the Yuchi tribe were fluent.

The research is funded by the Australian government, U.S. National Science Foundation, National Geographic Society and grants from foundations.