No shipping method selected notification

I followed instructions on thread http://www.zen-cart.com/forum/showthread.php?t=39376 to have no default shipping method on checkout first page.

If customers try to click on Continue without selecting a shipping method, zen cart just sits on the same page without a "missing shipping selection" notification.

Any help to accomplish that?
Thanks in advance

In the file:
/includes/modules/pages/checkout_shipping/header_php.php

You could add the code in RED:

// process the selected shipping method
  if ( isset($_POST['action']) && ($_POST['action'] == 'process') ) {

    if (!$_SESSION['shipping']) {
      $messageStack->add('checkout_shipping', 'Please select a Shipping Module', 'error');
    }

Thanks Linda, it works.
I completed it by managing multi language:

 if (!$_SESSION['shipping']) {
      $messageStack->add('checkout_shipping', PAGE_CHECKOUT_SHIPPING_CORIMTEC_NOTIFY , 'error');
    }

Thanks for the update that this worked and for posting your solution for multi language ...