setLocale() doesn't change the language set by browser

in the BaseController I did this:

PHP Code:

    public function initController(RequestInterface $request, ResponseInterface $response, LoggerInterface $logger)
    {
        // Do Not Edit This Line
        parent::initController($request, $response, $logger);

        // Preload any models, libraries, etc, here.
        $session = \Config\Services::session();
        $language = \Config\Services::language(); <--------- Added This
        $language->setLocale($session->site_lang)  <--------- Added This;  
        // E.g.: $this->session = \Config\Services::session();
    } 


in app/config/Lang.pgp

PHP Code:

<?php
namespace App\Controllers;
use CodeIgniter\Controller;

class Lang extends BaseController 
{
    function __construct() 
    {
        //parent::__construct();
    }

    public function index()
    {
        session()->set('site_lang',  "pt");
        //$this->load->view('welcome_message');
    }

    public function switchLang( $language = 'pt' ) 
    {
        session()->set('site_lang', $language);
        //header('Location: http://localhost/ci_multilingual_app/');
    }
}