There is no site-wide standard in regard to American English versus British English. A best practice would be to follow what is primarily used in the country from which the article's subject originates. However, within articles maintain consistency by not switching back and forth between American and British English.
If the country of origin for the article's subject either does not have English as an official language or uses a less common dialect of English, the default is British English for European countries, but otherwise use American English.
In terms of dialect words, please could these be kept to a minimum as they compromise the encyclopediac quality of the wiki, and this wiki does not use standard english only, and there is no error with using technical terms.
Technical limitations: There are exceptions to this that are, alas, numerous. One such example would be apostrophes ' since they conflict with wikitext. It's best to avoid single 'quoted' words when you are applying bold formatting. Placing four apostrophes around a word as if to put bold in quotes, ''this'' confuses MediaWiki and produces 'this'. (Plural possessives make fixing this problem doubtful: 'examples' = 'examples'.) Use double-quotes " instead, even if you usually use apostrophes for highlighting technical/slang/nicknames.
For tech-savvy users, the HTML ' entity doesn't work because the Visual Editor replaces them with Unicode (substitutes the code with ' ). However, the typographically correct single quotes ‘ ‘ and ’ ’ do work, but are a pain to keep typing. See, Help:Custom edit buttons.