protestant west slavs are interesting and have been pointed out.
This might seem like a cop out but there were many attempts OTL to set up Huguenot french colonies in the new world, lets say they have more success and we could see some sort of french speaking protestant state in the americas, however they might end up speaking something more similar to creole than an original romance language.
As much as I like the idea of New France becoming the Paraguay of North America, more French colonization of Native American lands would've put an end to the first colonists' policy of not treating the locals like shit - they were French drops in a Native American sea, and needed to cooperate with the nations and tribes of North America to make a profit and, you know, not die. Actual colonization not restricted to isolated forts and a handful of fur trappers with a worrying penchant for adopting local customs, by believers in a religion as aggressively fundamentalist as early Calvinism... yeah, New France would've become even worse than the Thirteen Colonies fairly quickly, and Parisian French would've become the language of the land instead of any kind of creole.
Huguenot France and Hussite Bohemia are doable, however.
Parts of northern Italy could've become Protestant as well - the OTL Province of Sondrio was about to adopt Protestantism while under the rule of the Grisons, but said experiment ended in a massacre; Milan had a few heretical movements of its own, like the Pataria, whose remnants could've joined the Protestant cause if they'd survived; Venice's always had a troubled relationship with the Church, and the Savoy lands were rife with heresy and heterodoxy, from the Cathars to the Waldensians and, of course, they bordered Calvin's own turf.
Last edited: