I feel like the Vampire Court in Monster High still functions a lot like the Roman Empire did. Like yeah they have a queen, but there's a council/senate and governors and stuff.
And I think Latin would still be a very prominent "official" language that they use as a standard for important things (especially with the ancient elite). Like they speak Romanian and Hungarian and Ottoman Turkish and stuff. But Latin (and/or maybe English) would be the language that "all" vampires would know so that's the one for decrees and laws and stuff.