The plural of "forum" is...

Please forgieve this non native English speaker for butting in this discussion, which isn't by far new in these forums/fora.

English is a living language and, as such, always evolving. As John has already noted, there are quite reputable dictionaries that accept "forums" as the proper plural of "forum". To me, this indicates that normal usage has incorporated "forum" as a proper English word of Latin origin, and therefore the word follows the normal English rules for forming plurals.

Incidentally, the cases of "data" (plural of "datum") and "media" (plural of "medium") show that things can be more complicated. I wonder how many people would say "This is the only datum I have" or "The Internet is the fastest growing medium of them all".

Your message is quaintly comical since you quote Latin and tell us "that's English".

The Oxford English Dictionary give forums as the first plural and fora as secondary.

C'est la vie!