Translation widget that appears in your blog's side bar. Readers can translate your blog into 10 different languages, automatically in one click.
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+.
Shows only posts and pages regarding the client's language.
Helps you create links between equivalent (but different language) pages between WordPress installations.
This plugin adds a standard compliant language tag to your post and page.