This Wikipedia article should be what you're looking for.
A good chunk of the countries use DMY format (i.e. 2 August 2015), so using that would cover a pretty large amount of people. Quite a few also use the YMD format (i.e. 2015-8-2), however, and America uses the MDY format (i.e. August 2, 2015 or (less commonly) with an ordinal: August 2nd, 2015).
Also, each country differs in not only the order but the formatting as well. For example, some use only numbers, while some use the name of the month as well.
Luckily however, many programming languages and frameworks (such as Microsoft .NET and Java) have a built in formatter so that you don't have to format it by hand.
I couldn't find anything specifically about formatting date ranges in different cultures, though. However, the EN dash is made for use in ranges (see this answer).