There was once a separate social enclave in every river valley in the world. In each one a language grew. The languages borrowed from each other, and became similar, and over larger distances, evolved in different directions and became dissimilar. So did the social enclaves. Migration, voluntary, and forced caused the languages to mix, and left behind small regions where the unmixed originals were still spoken, only to be mixed with the languages of later invaders.
So, eventually, a single range of hills, or even mountains were not the barrier that once they were. Rivers were crossed, and even seas, and the small languages were assimilated and became larger languages. In Nigeria, today, there are still five hundred languages, many spoken only in a single small valley, or village. These language will never assimilate the dominant languages of the world, and as the children of those cultures become more cosmopolitan, they will speak other languages more and more in preference to the language of their homeland. Just as it happened to the two hundred and fifty languages in California, there will simply not be enough native speakers for common conversation. Grandparents will not be able to tell their grandchildren the tales of their people in their own language, because the children will not speak the language. So, the language dies.
As they die, other languages, such as English, (which absorbs terminology and expression with an astounding facility) will assimilate apt expressions from them. People on patios, noshing hors devours will build verbal mausoleums to languages they never knew.
Tris
“Language is not an abstract construction of the learned, or of dictionary makers, but is something arising out of the work, needs, ties, joys, affections, tastes, of long generations of humanity, and has its bases broad and low, close to the ground.” ~ Noah Webster ~