WordPress - Change language programmatically via url

function.php

<?php
function wpsx_redefine_locale( $locale ) {
        $lang = $_GET['lang'];
        if( $lang == 'en'){
          $locale = 'en_US';
        } else {
          $locale = 'pt_BR';
        }
    return $locale;
}
add_filter( 'locale', 'wpsx_redefine_locale', 10 );