how can get variable from config file in CodeIgniter i need in controller

I have this code in config file:

if (isset($_GET['language']))
{
    $language = base64_decode(strtr($_GET['language'], '._-', 'ABCDlanguage48+/='));
    $_SESSION["language"] = $language;
    $config['language'] = $language;
}

And I need $language in controller __construct function. How can I achieve that?