I'm sure you're also aware that there are WP rules about this.  I'm hopeless with tracking down our rules and policies, but my understanding is that where the subject is clearly American, say, then American spellings and word usages are employed.  Where it's clearly a Brit, then British words and spellings are used.  And so on.  Where it's a general topic such as Gregorian calendar, one version of English applies consistently.  It's usually the version used by the originating editor that remains, but a consensus can decide otherwise.  So you might have Gregorian calendar written in New Zealand English, and Julian calendar written in Canadian English.  All OK, as long as people know what's going on.  I've often thought that articles on general topics should have a banner: This article is written in British/Australian/American/Jamaican/whatever English, so that editors would become aware, firstly, that there are in fact different versions, and then they'd be more alert to using the words that fit best.  Assuming they know what they are; which in many cases they may not.  But other editors will soon come along and correct things like alternate/alternative.