I simply have not heard of Any other countries in MLP... They always mention Celestia as the ultimate Ruler of the world. Or as a God.
And I do understand One country and one World, but then I would rather make the symbols more of a world. The Hammer and Sickle is mainly a banner of Revolution, one we have as long as the bourgeois is in power, since it is the Peasants and the Workers uniting against their oppressors. But then, That is just my opinion. There are enough variations of Social, Commun and Marx-ism to collect most of our Opinions.
But ... in Heart Warming Eve episode they left old land and found new one and called it Equestria, so i dont think Equestria is entire planet Maybe in further episodes they will mention other lands... but thats a maybe heh