public static function getInstance()
 {
     if (empty(self::$instance)) {
         self::$instance = new self();
     }
     return self::$instance;
 }
<?php

require_once 'classes/Preferencias.php';
$p1 = Preferencias::getInstance();
print 'Alinguagem é: ' . $p1->getData('language') . "<br>\n";
$p1->setData('language', 'pt');
print 'Alinguagem é: ' . $p1->getData('language') . "<br>\n";
$p2 = Preferencias::getInstance();
print 'Alinguagem é: ' . $p1->getData('language') . "<br>\n";
//$p1->save();