I present this as by-no-means a complete argument, but a very salient point imo is the notion of the 'accent'. It is the most prominent etymology mutation in language (driving inter-language variance between adjacent cultures), and exists not only in the human but in the animal kingdom. Its basis? The maxillofacial expression of the most dominant speaker(s) within a group, which shapes their vocal inflection and passes to the wider culture by social effect.

Regardless, the fluidity of language is self-evident to an extent : it is partly embodied in the entire concept we call figures-of-speech (a linguistic phrasing can be literal, or sarcastic, or described by metaphor, ...). Partly in the common reality that our dictionaries list multiple possible definitions for many words. Partly in the fact that (many) synonyms exist. Partly in sheer human individuality.