Either is possible. I feel comfortable with forums for some reason, perhaps because fora sounds faintly like something that would attract a gathering of botanists (the antithesis of boaters in my experience).
I had a good row aboutthis with a headmaster. He insisted on using latin plurals which started with his use of the word "croci" to describe the flowers in the school garden, and finished with a row about the lack of definition in latin for the plural of virus, which is viruses in English according to the OED, indeclinable in the plural in latin, following 2nd declension neuter for singluar or plural.
The rule is "if in doubt, anglicise". There is no hard and fast rule, except that generally the latin plural form is used if using the latin on purpose, or refering to more than one forum.
On a lighter note, of course, you can simply folow the example of a man who wanted to buy twoo mongooses and wrote the zoo. But he then realised that he might be mistaken, so rewrote the latter asking for two mongeese. Eventually he just ordered one mongoose "but while you're about it send me two".
Think perhaps you are mixing up the 2nd declension masculine (where the nominative plural is indeed -i) with 2nd desclension neuter (as in forum) where the plural is as TK correctly defines is -a, hence fora. Latin dictionary will show "forum, fori" this second word being the gentive singular, not the plural.
S**t - I couldn't get into Cambridge over 40 years ago 'cos I couldn't get me head round Latin and now it seems to be a requirement to take a full part in these forxx
It must be forums. It would only be forae if the Latins had had computers. On computers its all American or English if you are lucky.
Talking about the Romans having computers: Driving along what was obviously an old Roman Road - straight as anything - we go over a railway bridge. My Dad was driving and turns to my new girlfriend (who at the time was taking History at University) and asks "This bridge is only about 50 years old, so have you any idea how the Romans crossed the railway?". A long discussion ensued about railway crossings and legionaires feet wearig the rails away.