You're making the claim, so it's your job to prove it, not ask some AI and get your opponent to do the legwork. Moreover I skimmed ECMA-376[1] and it doesn't mention anything about locale-invariant encoding for function names. The only mention was for the CELL function, which could accept multiple values depending on locale.
For the purposes of this conversation I'm pretty confident what ChatGPT said is correct, feel free to look it up in case you doubt it.