When money is discussed in a book, what currency should be used for a book translation covering many countries?
I've had similar issues with translating currency in the past.

I believe that as a general rule of thumb, if the text has a worldwide audience, using US Dollars is the best choice. Many countries will have a general grasp on the value of USD and those who don't can simply use conversion tools to guide them. If the book applies to a more narrow geographical area, you can use the currency for that area (e.g. Euros for a European Audience)

No currency is accepted and understood worldwide. However, US Dollar is probably more global than the rest.