When getting to know her at first, if you want to chat casually in the bar, you could be there to translate. I’ve done that with guys from China. When it comes to negotiating, a lady is required to have a second in her room if there are to be two men there, for security reasons. It’s also acceptable to write things down- or as Flint suggested, email the lady a bit and you can help your friend with what he wants to communicate that way. I’ve also had a French man who used a translation app for questions he wasn’t sure how to ask in English.