It is English, not Latin, that decides whether the plural of some word ending in -um is -a or -ums.

ECONOMIST: Johnson: Don't shoot the pian-ist | The

What made it most amazing was that she had spoken articulately, no ums and uhs, no telepromper, no groping for words, for more than forty five minutes without so much as a note.

FORBES: My Lunch With Lady Margaret Thatcher