Since I see "MC" often in the context of English games and so forth, I wanted to know if Italians had an equivalent word that they would use when talking about a character/protagonist of a story, especially if used by gamemakers themselves.
I have been a part of the Italian pen and paper role-playing community for over 20 years. In that context, when a player is referring to their own character, or any character controlled by another player, the acronym you are looking for is PG, which is an abbreviation of personaggio or personaggio giocante (here is one of many examples you can find in online forums). For characters controlled by the Game Master, i.e. non-player characters, the Italian community has had a hard time deciding whether to go for the globally understood NPC or the translated PNG - personaggio non giocante.
An example from the last link reads
[...] il compito del DM è quello di gestire tutto ciò che non sono i personaggi giocanti (PG): i personaggi non giocanti (PNG) e mostri che popolano il mondo, i luoghi, gli eventi, le conseguenze delle azioni [...]
What is interesting though is that I have never heard the use of "MC" in English settings, but only "PC" - player character.
I think that English people tend to use acronyms much more than what Italians do; moreover, nowadays, there are many specialized sectors, each one having their 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.