I think that English people tend to use acronyms much more than what Italians do; moreover, nowadays, there is a lot ofare many specialized languagessectors, each one having itstheir own acronyms. Being English the language used worldwide, it is exposed to such inflections way more than other languages.
That being said, I don't know much about game makers but I think that no, the MC would be called protagonista while another character (not the main one) would be called personaggio. Or, even if writing in Italian, a game maker could use MC, but only considering that its intended audience would understand it as a specific term used in that peculiar context.