A copy editor.

I copy-edit articles according to Wikipedia's Manual of Style. My speciality are national varieties of English.

I mostly edit articles that use British English (British spelling in the headword, strong ties to British English, or predominantly written in British English). I also copy-edit articles for consistent American, Canadian, or Australian spelling.

Canadian English and British English with Oxford spelling (-ize, not -ise) are (IMHO) good choices for articles when a more neutral variety of English is desirable. IUPAC spelling (UK or US) should be used for chemistry articles (consistently sulfur, aluminium, caesium).

Thoughts on why ENGVAR templates should be actively used, especially for non-US varieties:

The majority (not an overwhelming one, but a majority) of Wikipedia editors including non-native English speakers appears to use American English (which is fine, of course). But this causes articles that are edited in British English or other varieties to drift towards American English over time, because many editors don't care about the variety of English being used. Others make good-faith "corrections" to spellings unknown to them. ENGVAR templates are useful indicators to maintain consistency.

I use script-assisted editing with high-quality wordlists to assess which variety of English is predominant in an article and to quickly find inconsistencies in articles where the variety of English is already established.

Also read this: ENGVAR templates - an overview