DiceLock Comment Translator inserts a language translation form at he bottom of your posts, pages and categories. The forms makes use of Google transl
Allows you to blog in multi-language, and users to select which to read. Works on every blog UI elements, not just the post.
Babel allows you to write your blog contents in multilanguage.
Gengo is a full featured plugin that provides multi-language blogging for WordPress 2.5+.