Don't worry if you're not familiar or comfortable with the local English variant of a destination article: just write in the style you're accustomed to and somebody will probably come along later and correct it - that's one of the benefits of wiki editing!
If the article concerns a destination that has no history of using English and no clear preference for the variety to use, we prefer US English spelling. This isn't because US English is somehow better (although US spelling usually is shorter) or to stomp on the rights, heritage, and cultures of other English-speaking countries. We just need to pick one default spelling style for consistency in the same article.
Many of our non-destination articles were written in Commonwealth English and should not be arbitrarily changed to the US variety. Usually it's not a good use of your time to go right through an article to standardis(z)e the spelling unless preparing for a star nomination or for off-line publishing. If you are preparing to do this for any destination outside of the regions listed above, it's best to first discuss which variant you are going to use on the article's discussion page.
Reference guides for US English spelling:
Occasionally proper names do not follow local spelling conventions. These words should not be changed -- the proper name should not be mangled to conform to Wikitravel's spelling rules:
It can be helpful to other editors to use an HTML comment to mark incorrect spellings which are preserved in proper names:
* Joaquin Miller's home, "''The Hights''"<!-- sic -->, rests on the heights of the Oakland hills.