Error on $ci =& get_instance();

[eluser]PermanaJ[/eluser]
I got error on line '$ci =& get_instance();'

the error message is

Fatal error: Call to undefined function get_instance()

Anybody know how to solve the error? I want to extends Language class so it load language base on cookie

Code:

class MY_Language extends CI_Language{
    
    function MY_Language() {
        parent::CI_Language();
        
        $ci =& get_instance();
        $language = get_cookie('language');
        if( $language ){
            $ci->config->set_item('language',$language);
        }else{
            set_cookie('language', $ci->config->item('language'), 1447);
        }
        $ci->lang->load('myword', $ci->config->item('language'));

    }
}