r1599: Fixed bug://report/97. If a user had selected a language that had since been deleted, the email notification system would fail because the template paths it would try to load wouldn't exist becuase the langcode wouldn't be added.
* docs/changes.txt
* include/class_notification.php:
(NotificationCenter::_localeFromUserId): Instead of checking if the language ID exists for the user, get the langcode for the user's language and check if *that* exists