public static function setDefaultTranslator($translator = null)
    {
        if ((null === $translator) || ($translator instanceof Zend_Translate_Adapter)) {
            self::$_defaultTranslator = $translator;
        } elseif ($translator instanceof Zend_Translate) {
            self::$_defaultTranslator = $translator->getAdapter();
        } else {
            require_once 'Zend/Validate/Exception.php';
            throw new Zend_Validate_Exception('Invalid translator specified');
        }
    }