Research about the threshold of a linguistic 'slippery slope'?

[Nicholas Ostler]

Dear All

This is a question, rather than a bit of transmitted news.

It is sometimes claimed that there is a critical proportion of speakers 
of a given language in a multilingual community that must be maintained, 
if that language is to continue in everyday use. Such a claim makes 
sense in a context where there is a background metropolitan language 
(typically English, but it could as easily be Portuguese, Russian, 
Spanish or Chinese) that is under no threat, and spoken by numbers 
approaching 100% . The other, less widely spoken, language can only 
survive in stable bilingualism with this background language if there is 
a fair presumption, within a given community, that enough listeners are 
there to understand it.

The idea, then, is that there is a kind of tipping point, or a threshold 
of the slippery slope, perhaps as high as 70%; if the lesser-speaking 
community dips below this proportion, it will tend to diminish further, 
until (without active policy measures) it might die out altogether. But 
above this proportion, its numbers can vary up and down with no 
long-term effect or trend visible.

Is there a percentage figure one could give, and if so is there any 
research that bears directly on this point?

Nicholas Ostler

-- 
Foundation for Endangered Languages
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