> Those outside of the US who subscribe to this ideal seem heavily influenced by US culture in my experience. I'm not aware of non-US sources of the idea.
In ancient Athens they spoke (ancient) Greek, so no they didn't have an ideal of "free speech", as in the modern US, they had ideals of isegoria and parrhesia - separate concepts that Athenians at least recognised were often irreconcilably in conflict with another. Any such nuance is completely lost in most modern applications.
I think it unlikely that Ancient Athens was heavily influenced by US culture on the topic of free speech as an ideal: https://www.britannica.com/biography/Socrates/The-Athenian-i...