TLDR: There are no official standards. It's at the discretion of the company and maybe influenced by brand guidelines. However, large international organizations seem to favour European format (e.g. 4 August 2015) presumably because it's used in more countries.
A quick search on "International English" suggests spelling-wise, you should be referencing "Oxford English", which has been adopted by majority of international organizations.
'Oxford spelling' is used by the principal and most prestigious English dictionaries such as the Oxford English Dictionary, the Collins English Dictionary and the Cambridge dictionaries, as well as by prestigious publishers and publications and a host of international organizations, such as Oxford University Press, Cambridge University Press, Penguin, the Encyclopaedia Britannica, Nature, the United Nations and all of the bodies that report to it (such as the World Health Organization, the International Labour Organization, UNICEF and UNESCO), the World Trade Organization, the International Organization for Standardization (ISO), the International Atomic Energy Agency (IAEA), the Organization of the Petroleum Exporting Countries (OPEC), Interpol, the International Committee of the Red Cross, World Wide Fund for Nature (WWF), Amnesty International, the World Economic Forum and NATO, among others.
taken from http://www.upf.edu/gl/en/criterisupf/oxford.html
Oxford English however is about spelling and does not provide specifics on date formats.
From a quick scan of the websites of these organizations, it seems like the European format is preferred. (e.g. 4 August 2015).
This makes sense because this is the preferred format for majority of countries around the world.
However, date formats for content within larger organizations are typically controlled by marketing brand guidelines to maintain consistency across all communication channels. So you might want to check in with your marketing department prior to choosing the format.