Number/Date/… Standards for International English

We don't know (yet) where the user is located (browser detection is out of the question), so the user need to go from a global site to a country-specific site to select their prefered language and local.

In the global site, we will offer an English International website (https://en.wikipedia.org/wiki/International_English). The problem is I can't found any standards for date and number (separator). If there's any, what standards should I use?