Change Default Language

Hello All,

      I'm in the last step of translation. I want to now change default language and make it chinese. But i dont know how to change default language.
     I have tried changing settings.php as $conf[] = array('site default => 'zh-hans'') and also tried $[i18n_languages] = array (site_default => 'zh-hans' ).
     But none of the above worked.

So , can anybody give me solution? I want to make site as drupalchina.org.
 
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Thanks & Regards

    Vishakha