Originally Posted by Jhangora
I think language is a very good definition of a people. About half of the languages spoken today will die out by the end of this century ---> Endangered Languages Project
Maybe not the total definition, but a people losing its native language definitely marks the end of them as a separate ethnic group, and the beginning of assimilation into a larger ethnic group, which may very well end with all the distinct cultural features and the identity of that people vanishing.
Which is why a people wanting to preserve their language is way more than just "so they don't want to communicate with everyone else. Who cares?" which is the attitude you see a lot about language death.