"

You're correct: not all Chukchi people speak Chukchi. While 15000 is about the right figure for the number of people registered as ethnic Chukchis, I suspect that 10000 speakers is wildly optimistic. But I'm not aware of any accurate count. The census figures overestimate too, since the question about native language can also be interpreted to mean ""what is the language of your ethnic group"".  "