Ehm, hur menar du med att "använda" flera språk, att du ska skiva på flera olika språk, eller översätta? Det finns annars en till flera populära WP plugins för det.
WordPress Global Translator Plugin by Nothing2Hide is one of the most popular translation WordPress Plugins. It is a stand alone WordPress Plugin, which means it doesn’t require any additional files to work. Just activate the Plugin and it puts a small table of international flags in the header of your blog which, when clicked, will translate your blog content into that flag’s language.
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There are two types of WordPress Plugins to help cross the language barriers. Translation Plugins provide instant translations of your post content into other languages. Multilingual Blogging WordPress Plugins allow multi-lingual bloggers to blog in more than one language. You can use one or both types of WordPress Plugins together.
http://lorelle.wordpress.com/2007/02/05/translation-and-multilingual-wordpress-plugins/