[support] Sending email when translation flagged as out of date

In Drupal 6, I want to send an email to all people with the "translator" role when a translation is flagged as out of date. I'd have thought this was a fairly common task, but I can't seem to work out how to do it as there's no trigger for translations. Do I need to create a trigger in my custom module? Is it easier to install Rules and use that to handle this or is that overkill for one feature? Is there anything I'm missing?