My experience is that GPT-4 is quite good at most languages, including hard ones like Chinese - especially when paired with a “verification” step, where you copy something it wrote and start a new session and ask, “Is this sentence well-written <language>?”

It has a surprisingly deep understanding of nuance and context. You can copy some Chinese text that Google Translate completely fails to translate, paste it into GPT-4 and ask “Please explain this text including any nuanced meaning that a foreigner would miss“ and get a detailed, coherent explanation.