Paleolinquistics is actually super-complicated because one is continuously re-thinking the work of older scholars who made all kinds of assumptions based on the monoculture they saw all around them… despite the fact they speak Latin and Ancient Greek themselves.
In fact most people worldwide speak two or three or more languages, even today.
And archaeology suggests a distribution of cultures far different from what we expect from historic times and far more varied – centralizing, normative forces being the exception rather than the rule – and then what there were, may not have been geography-based… Consider the Bell Beakers, and their archaeology, and possibly with a historical overlap as the Celts that we know… Consider, too, the organizational forces that governed the Druids over all of Europe, as an example of how prehistory can be alien to us, and unfathomable…