I don’t think the person needs to be bilingual. They could just speak English, and start with whatever English attempt at translation had already been made, then take a look at an LLM translation, and then create the final copy based on all of that. They don’t need to speak Mandarin.

I always thought there might be a market for this kind of service. Maybe it would be hard to build trust though. If they don’t trust your language and copy creating abilities, no one will pay for your English skills. And how are they supposed to assess your abilities when the problem they are facing is that they don’t have good command of English in the first place?