Yours is a broad spectrum of answers' question.
There is a thin red line between what is a purely technical translation advice and one with a marketing insight. When the client has a clear idea on the second one, you just need to push them to define the limits as they may just be looking for a translation service and the aspects of localization related to it (language flavor, metrics use, decimal notation, currency symbols, etc.).
If they are lost and have no idea, you may need to offer a marketing research support that goes as far as a usability testing of the website to assess the acceptance of the target user.
I apologize for my summary, but a lot could be written and maybe you could help with a description of your specific problem.
