There is potentially a character for every country that exists now or ever has, even ones that were never independent countries like Hong Kong, and supernational states like the Holy Roman Empire. The human names are technically not canon, but nonetheless are mentioned (although they are Word of God they're not used in the manga aside from two dubious instances in strips and one of the image songs note France's "Embrace the tres bien moi" opens with the line "Bonjour. Je m'appelle Francis"; they don't appear on the website and they were deleted with the author's original site blog). Nevertheless they're popular in fandom, mostly because many people don't like using the actual country names in fanfic. It also helps that he's open at least to the idea of human names.
And given how many there already are, as well as the real life world history, it should come as no surprise that the original main characters (Germany, Italy, Japan, America, England, France, Russia, China) have been supplemented by a whole world of major, minor and periphery characters. It's reached the point that finding out who the main characters are is a largely moot point (unless for formality's sake) when a good chunk of the ensemble have been given fandoms and their own time to shinenote Due to the very nature of the series and history itself, each Nation (at least for the more prominent ones) is technically his/her own main character.