There has recently been a suggested edit to: Can I buy my friend a gift I am also going to buy a copy for myself?, in which the changes suggested followed American usage and spelling rules. The post itself was essentially correct in British usage. Should we use a standard style (US/British), or should such considerations be based on the regional tag of the post?
All variants of English are acceptable.
'Correcting' American English to British English or vice versa isn't a good edit. People are free to use their own dialect of English; edits should focus on making improvements to the post rather than changing its local style, provided it's intelligible.
Does [SE] have an accepted standard on language and spelling? Which is it?
For bodies, no. For tags, US-English.
Titles don't actually need to be consistent (tags absolutely do!), but if you think anyone might want to search for a question then you would do well to use the more common spelling - whichever that might happen to be...
Note that changing the spelling of language keywords or identifiers to match the spellings actually used by the relevant language or library is very much appropriate!
-- Shog9, Community Manager
With other sites on the network (Namely Chemistry SE, I haven't seen it elsewhere (I'm not very active elsewhere)) it generally doesn't matter. The proper etiquette is to keep it in whatever variant it is in. So if the OP uses UK English, then someone cannot come along and make it US English.
(Having realised I was the one to correct it to UK English this sounds weird, but I didn't realise at the time what I was doing, I generally only remember color/colour and other "ou" variants)
In Portuguese SE, it is considered extremely rude to suggest an edit that attempts to erase a certain variant. Users who try this have their edits rolled back and are politely called out on chat or comment.
I personally agree with this procedure, and urge the community to rollback or reject edits that do so, even if they address other, non-regional issues.