Since you are using the users model to save the record, it would be hard to not send the email. You would either need to write your own code to save the user or extend and override the model.
Easier way is to just make sure that the com_users language file is loaded, so those capitalized strings get replaced with the correct text, like so:
$lang = JFactory::getLanguage();
$extension = 'com_users';
$base_dir = JPATH_SITE;
$language_tag = 'en-GB';
$reload = true;
$lang->load($extension, $base_dir, $language_tag, $reload);
I'd put this after the require_once
that loads the model and you should be good to go.