I've always been a big fan of IDEA's ResourceBundle editing feature. I think it's great, easy to use an really helps to get a vision of all properties in one view.
I realized it would also be very useful for editing group of properties that are NOT i18n but that share the same keys.
In my present case, I need to edit property files that are linked to an environment (DEV, TEST, PROD etc.). I've tried to name them like filter_PROD, filter_TEST but IDEA won't recognize them as part of one Bundle. Too bad....
It'd probably be quite simple to base the automatic Bundle creation on some syntactical pattern. And if not, well, give a way to developer to create the Bundle themselves.
Hope that's on next IDEA version feature list :)