If you have an API, and you are a UK-based developer with a highly international audience, should your API be
setColour()
or
setColor()
(To take one word as a simple example.)
UK-based engineers are often quite defensive about their 'correct' spellings but it could be argued that US spelling is more 'standard' in the international market.
I guess the question is does it matter? Do developers in other locales struggle with GB spelling, or is it normally quite apparent what things mean?
Should it all be US-English?
I would tend to use US-English as that has become the norm in other APIs. Speaking as an English programmer, I don't have any problem using "color", for example.