Wikipedia should not only accept UK and US spelling, but also minority spellings such as Canadian.
According to the Wikipedia MoS:
Neutral spelling if possible (spelling a word in a way that is recognized everywhere)
Preserving spelling in proper names (you can help!)
Articles about topics specific to an English-speaking country should conform to that country's spelling and usage.
In all other cases, the spelling used by the first major contributor should be followed. If, however, an article has been stable for a long time using a different spelling, the spelling shouldn't be changed back to the first major contributor's spelling. (Second sentence is not part of the MoS at the moment.)