The Google Ajax Translation WordPress plugin provides a quick, simple, and light way to add translation to your blog.

A “Translate” button can be added to the bottom or top of posts, pages, and/or comments. When the button is clicked, a popup window opens showing a list of available languages. You can choose which of the 43 languages to display in the Administration Panel. The list of languages can be shown as text, as flag icons, or as both.

You can get this plugin form here