I think this may have to wait until the sprint, when we can discuss it with Nikerabbit.
There is no hurry. I know only of this one example. Do you know if many translators download the po-files? If so, it might be a good idea for me to temporarily add a warning to the English page. Ideally it would of course be better to have such text in the Talk page, but I don't think it will be much help there - most likely, translators won't think to consult the Talk page for such information.