Don't worry if you're not familiar or comfortable with the local variant of a destination: 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!
Usually it's not a good use of your time to go right through an article to standardis(z)e the orthography 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.
If the destination 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 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. Below are reference guides for US English spelling:
Webster's New World College Dictionary, Fourth Edition, Wiley Hoboken, N.J.
Webster's Third New International Dictionary, Merriam-Webster, Springfield, Mass.
National Geographic Atlas of the World, National Geographic Society, Washington, D.C.,