Language

Countless different spoken, written, and gestural languages were used by different cultures throughout time and space.

The Doctor had great expertise in linguistics, once claiming to be able to speak five billion languages. (TV: The Parting of the Ways) However, they still utilised the translation circuit of their TARDIS while travelling through space and time, though this was often more for the benefit of their companions. (TV: The End of the World, Cold War)

Language was constantly evolving. When Jo Grant invented the word "telempathy" to mean a sort of telepathic empathy, and asked the Third Doctor if this was a word, he responded that it was now. (AUDIO: The Tyrants of Logic)