Selected language in URL

How I can make URL on my site look like http://example.com/lang/controller/action, where ‘lang’ is selected language (for example, ‘en’ or ‘es’)?

May be with .htaccess, but I don’t know what to write to it.

Using my extension :rolleyes:

http://www.yiiframework.com/extension/langhandler/

Thank you, sidewinder. Good extension.