If you are using Joomla! 1.7+ stop right here. Joomla! 1.7 is now equiped with a language selector tool like Multilang M17n. The objectives of Multilang M17n are now part of the core of Joomla! 1.7+

Please read this carefully: http://community.joomla.org/blogs/community/1468-multilang-in-17-whats-new.html