My question is, Once these words enter English, how obligated are we to follow the original language in pluralization - or, for that matter, any aspect of their use, including their original meaning?
Good question. I guess we're as obligated as we want to be... for instance the usual plural of
forum is
forums and not
fora, and
data is often used as a singular mass noun.
zucchini, broccoli, spaghetti are often used with singular verbs.
very was borrowed from a French word meaning "true".
There are a lot of words that are plural in their original languages but that are uncontroversially singular in English: agenda, erotica, opera, candelabra, paraphernalia, trivia, graffiti, candelabra, stamina.
The belief that we must look to another language to discover how to use English words is known as the etymological fallacy.
