It was common in Victorian-era English for a Latin word and its Latinate plural to be imported into English.

Victorians understood "forum" to refer to a place at the centre of Imperial Rome, not to an activity, so they imported the word but not the plural.

The Victorian practice of plural formation in English was abandoned. With the explosion of knowledge it proved too difficult to know the origin of a word in order to form its plural. Whereas Victorians would need to determine if "platypus" had a Latin or Greek or other heritage (is it "platypii' or "platypodes"), we say "platypuses".

Widespread use of "forum" in the modern sense of a "meeting" rather than a "meeting place" dates from the 20th century civil service. This use requires a plural, and this later use obeys the later English rules.

Use of "fora" is generally read as indicating the writings of a poseur: its use is not required for any grammatical reason, so its use must be to give an impression of High Culture. The Register delights in puncturing puffery, so use of "fora" is never going to be part of its robustly and defiantly Saxon house style.

"Forums" isn't an exception: it's "viruses" not "virii" for the same reasons. The Register is sometimes plagued by use of "virii" but the infection is quickly suppressed :-)

Mr. Turner, the plural "virii" would be that of a word "virius". "Viri" would be the plural of "vir". The plural of "platypus" would be either "platypodes" or "platypi", not "platypii".

As a speaker of Latin I'm amused by both groups who have no idea of Latin: Those that need to throw in some pseudo-Latin to show off, and those that show off by incorrectly correcting the former group.

There's not much in this article to indicate that there's any real "gap" between behaviour on Chinese boards and Western boards.