Language is one thing and races are another.
Races are historically geographic in nature, a genetic isolate in breeding, while language is a function of culture. The two phenomena parallel and overlap each other, but seldom form crisp clean lines equating a language/race on one side of the line to another on the other side. Sometimes it seems as though languages themselves are the conquering invaders, crossing borders and conquering new territory even when the number of people involved is almost insignificant. Latin America is probably the best example of this, where a mere handful of Spaniards subjugated millions of Native Americans with fear, cunning, superior weaponry, and germ warfare. Though decimated, the natives’ numbers rebounded with the help of an admixture of disease-resistant Spanish blood. Nevertheless, much of the culture was forever lost, and Spanish and Portuguese are by far the language of the majority. Interestingly, one of the surviving native languages, Guarani’, is a national language spoken mostly by non-Indians. Though shrouded in the mists of prehistory, something similar must have happened in India, where ethnic Iranians (Aryans) spread far more language than bloodlines over the sub-continent and over time, still expanding into the future, having left vestiges all over Southeast Asia. On the contrary, people very similar racially might speak totally unrelated languages, as in the Caucasus and Africa. There Hamitic-speaking Hausas reside far from their Semitic linguistic cousins and tend to be ruled by Hausa-speaking Fulanis, traditional herders who have their own language but use that of their subjects when acting as rulers. A similar situation exists in Ethiopia, where very dark-skinned people speak languages related to the very light-skinned people across the Red Sea. Sometimes it seems a people adopt a foreign language simply because it’s an improvement over their own. This, the Celts seem to have done repeatedly in the history of Europe. It could certainly be argued that they’ve sacrificed their culture in the process.