CodeIgniter的多语言实现错误

I did multilingual processing using the codeigniter3 hook. It works fine on localhost. However, the server is failing.

This is the first registration question. Please understand that my question is poor.

PHP 7.2.19-0ubuntu0.18.04.1 (cli) (built: Jun 4 2019 14:48:12) ( NTS )
Server version: Apache/2.4.29 (Ubuntu)

I developed it by referring to the address here

// application/config/hooks.php
$hook['post_controller_constructor'] = array(
    'class'    => 'MultiLanguageLoader',
    'function' => 'initialize',
    'filename' => 'MultiLanguageLoader.php',
    'filepath' => 'hooks'
);

//application/hooks/MultiLanguageLoader.php
class MultiLanguageLoader
  {
      protected $CI;

      function initialize() {
         $this->CI =& get_instance();
          // load language helper
          $this->CI->load->helper('language');
          $siteLang = $this->CI->session->userdata('site_lang');
          if ($siteLang) {
              // difine all language files
              $this->CI->lang->load('header',$siteLang);
              $this->CI->lang->load('content',$siteLang);
          } else {
              // default language files
              $this->CI->lang->load('header','ko');
              $this->CI->lang->load('content','ko');
          }
      }
  }

//application/controllers/MultiLanguageSwitcher.php
class MultiLanguageSwitcher extends CI_Controller
    {
        public function __construct() {
            parent::__construct();     
        }
        // create language Switcher method
        function switch($language = "") {        
            $language = ($language != "") ? $language : "ko";
            $this->session->set_userdata('site_lang', $language);        
            redirect($_SERVER['HTTP_REFERER']);        
        }
    }

//application/config/autoload.php
$autoload['libraries'] = array('database', 'session');
$autoload['helper'] = array('url', 'file','cias_helper','security');

The helper keeps getting an error.
$ this-> CI-> load-> helper ('language');

I am getting these errors:

ERROR - 2019-07-27 17:33:13 --> Severity: Notice --> Trying to get property 'load' of non-object
ERROR - 2019-07-27 17:33:13 --> Severity: error --> Exception: Call to a member function helper() on null