Paris (AFP) - Economic prosperity is the worst enemy of minority languages, said researchers Wednesday who listed parts of Australia and North America as "hotspots" for extinction risk.Based on the same criteria used to determine the risk of extinction faced by animal and plant species, they concluded that about a quarter of the world's known 6,909 languages were threatened."Languages are now rapidly being lost at a rate of extinction exceeding the well-known catastrophic loss of biodiversity," the US-European research team wrote in the Royal Society Journal Biology Letters."Small-population languages remaining in economically developed regions are seriously threatened by continued speaker declines."In Alaska, for example, there were only 24 active speakers by 2009 of the Athabaskan people's indigenous language, which children were no longer learning.And the Wichita language of the Plains Indians, now based in Oklahoma, had only one fluent speaker by 2008.In Australia, aboriginal languages like the recently-extinct Margu and almost extinct Rembarunga are "increasingly disappearing", the team wrote."Economically developed regions, such as North America and Australia, have already experienced many language extinctions," they said."Nevertheless, small-range and small-population languages still persist in hotspots within these regions.