Change the language dynamically?

I am attempting to change the system language dynamically with a call to a controller method. I have in the view :

PHP Code:

<?php if ($this->config->item('language') == "francais") : ?>
<a href="changelangue?lang=english" data-js-langue>EN</a> 
<?php elseif ($this->config->item('language') == "english"):?>
<a href="changelangue?lang=francais" data-js-langue>FR</a>
<?php endif;?>

And in the controller I have this method:

PHP Code:

public function changeLangue(){

    if (!isset($_GET['lang']))
    {
        redirect("vehicules");
    }

    $this->config->set_item('language', $this->input->get('lang'));
    redirect("vehicules");
} 


I am being redirected, but the config language is not changing. It seems to always revert to the default language. I even tried changing it in the ' __construct' of the controller in question using the session userdata like so:

PHP Code:

public function __construct()
{
    parent::__construct();
    if (!$this->session->userdata('language'))
    {
        $this->session->set_userdata('language', $this->config->item('language'));
    }else{
        $this->config->set_item("language", $this->session->userdata('language'));
    }
} 


I have the language folders in system/language and in language.

Am I missing something?

Working With Locales

What did you Try? What did you Get? What did you Expect?

Joined CodeIgniter Community 2009.  ( Skype: insitfx )

Working With Locales

Hey thanks for your answer! I should have mentioned I am on 3.1.11. Unless someone officially rebukes it, there's no way to set the language in the config with it having a default value set up and redirecting from with redirect().

go  app/config/app.php 
chane like bellow 

PHP Code:

public $defaultLocale = 'en';

    /**
     * --------------------------------------------------------------------------
     * Negotiate Locale
     * --------------------------------------------------------------------------
     *
     * If true, the current Request object will automatically determine the
     * language to use based on the value of the Accept-Language header.
     *
     * If false, no automatic detection will be performed.
     *
     * @var boolean
     */
    public $negotiateLocale = true;

    /**
     * --------------------------------------------------------------------------
     * Supported Locales
     * --------------------------------------------------------------------------
     *
     * If $negotiateLocale is true, this array lists the locales supported
     * by the application in descending order of priority. If no match is
     * found, the first locale will be used.
     *
     * @var string[]
     */
    public $supportedLocales = ['en','fa']; 


for change  language  add header Accept-Language = En or ....
you can see i add header for angular code
 request.clone({headers: request.headers.set('Accept-Language',  'en')});

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