— “How did you say that I can save a Word document as a MediaWiki file?”
— “You need to download an add-on for Microsoft Word. Google for ‘save microsoft word document as mediawiki’.”
— “I did. It brought me to a page about OpenOffice.”
— “Hmm… Great success!”
In LibreOffice, the freer version of OpenOffice, saving as MediaWiki is already available without installing any additional add-ons. It may be so in the latest version of OpenOffice, too. I used this feature to upload to Wikipedia dozens of articles that were written by people who can write well, but don’t want to learn the complicated MediaWiki syntax.
For Microsoft Word there is the “Microsoft Office Word Add-in For MediaWiki“. I tried installing it, but it didn’t actually work. Your mileage may vary.
Aharoni in Unicode 
Yes, it’s a built-in export option in my OpenOffice (3.1.1.). Though I have never used it – I hate WYSIWYG. ;)