Put language index into URL Multilanguage CodeIgniter site - php

Question

My site is created in three languages https://anto-nguyen.com.
It works well to translate from one language to another one.
But.. I can't put the language indication into the URL.
I looked through all questions and answers that I could find here and have tried to use them, but unfortunatelly it doesn't work..
I use Controller LangSwitch
class LangSwitch extends CI_Controller {
public function __construct() {
parent::__construct();
}
function switchLang($language = "") {
$this->session->set_userdata('site_lang', $language);
redirect($_SERVER['HTTP_REFERER']);
}
}
The language is called by following code integrated into menu
<div>
<?= anchor(base_url("langSwitch/switchLang/english"), 'En'); ?>
<?= anchor(base_url("langSwitch/switchLang/french"), 'Fr'); ?>
<?= anchor(base_url("langSwitch/switchLang/russian"), 'Ру'); ?>
</div>
My .htaccess lookes like this
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /codeigniter/index.php/$1 [L]
And seems to be modified, but all suggestions I found doesn't work
Could you help me what to do that my link will appeared as /mysite/fr /mysite/en /mysite/ru?
All translation are in the folders language/english language/french language/russian
Mayby to change something in routes?
$route['default_controller'] = 'site';
$route['work'] = 'work/index'; //the URL 'work' will redirect to 'work/index'
$route['work/(:any)_(:num)'] = 'work/article/$2';
$route['404_override'] = '';
$route['translate_uri_dashes'] = FALSE;
$route['(:any)'] = 'site/$1';