One of my answers was changed; I agree with most of the changes but it also involved changing from british to american spelling (specialised -> specialized and initialising -> initializing). As a continental european, I have accustomed to writing in british spelling; Is this deprecated here?
The site language is 'English' but (within reason) the idiom of the original poster should be preserved. In particular, there should generally not be an issue with using either US or UK conventions on spelling. When editing, I would normally correct typos or make other changes in line with the author's intention, but would not change US/UK spelling and where adding any information always use the form chosen by the original author. (I am from the UK so prefer UK English, but if editing a post in US English leave that alone.)
The one more grey area is where the idiom rather than spelling might cause confusion. This is likely to be very rare, but where it occurs I would tend to look for a 'neutral' presentation (so avoiding either UK- or US-centric expressions).