Can't change Joomla Default language


On this site I want the default language to be Chinese. I set the default language to Chinese in the backend (it's got the star next to it) but when you went to the page you probably noticed that the site is displaying in english.

If you check the source code you will see on the very bottom hidden a var_dump of the language object, and by the looks of it the default is still en-GB

  string(5) "en-GB"

Why is this? Thanks

EDIT The default language is used when a language file in the requested language does not exist.

Still the problem remains, why does the site not default to chinese? you can change the language of the site and it works in Chinese中文版

EDIT 2 Even JoomFish say "Site default language: 中文版." In the administration...