I saw a really nice plugin at No Prerequisite blog. This plugin allows people to post in more than one language on their blogs using WordPress. This has been written in the form of a plugin. From No Prerequisite
The Language Picker Plugin is my personal solution for writing posts in more than one language. When activated, the plugin will display posts in either the default language (as configured in lang_picker.php) or in the visitorâ€™s preferred language, if available.
You can download the plugin from here and see the test post.