The WordPress Multilingual Plugin.
WPML makes it easy to build multilingual sites and run them. Developed by Amir Helzer of OnTheGoSystems.
WPML is a plugin for WordPress. Simply put, plugins extend the functionality of the basic WordPress CMS. In our case, WPML makes WordPress run multilingual.
WPML lets authors write content in different languages and translate content. It also includes advanced features for translation management and an interface for professional content translation.
Using WPML requires no technical or programming skills. Site admins can install it and turn their site multilingual, without any coding. WPML includes a complete API, for integrating with other plugins and translation systems. This way, developers can easily use WPML and turn their products into multilingual.