It was an old official art of Bronukon (Ukraine Pony convention) by maccoffee.

Source: >>2806707:https://derpibooru.org/images/2806707
And some other arts about them: >>2808702:https://derpibooru.org/images/2808702, >>2811515:https://derpibooru.org/images/2811515


I think each ponies present one country, do you have idea what countries are they stand for?

This is my presumption, but not sure (I presume they have to be Eastern European/Slavic countries)