Musea would be the correct Latin plural form. And you're right, you aren't obligated. It just weirds me out. :P
What's interesting is that your language does use the correct Latin plural form for datum. Except that you've practically forgotten that there's a singular form. ^^
Only because the English language borrows words and then rips them to shreds and poops on the shreds. :P It's a word borrowed from Latin, and the proper thing to do would be to also keep the Latin plural.
So wait, what's the English plural of museum? :|