I really have no idea what to make of this, but on one of the machines I've upgraded to El Capitan, all of the gatekeeper dialogs display without localized strings:
This displays after launching Chromium from the dock just after having replaced it with a new version by copying an app bundle from a DMG to the Applications folder.
This is clearly not expected behavior, but I'm not sure what I could do to fix it besides reinstalling El Cap (which I'm not too keen on doing if I can avoid it).
Has anyone else seen anything like this, and/or have any ideas for troubleshooting?