When the en-US version of a page is updated and that change needs to be incorporated in the localized versions as well (see bug 398355), there should be an easy way for localizers to access the en-US changelog/diff, e.g. a direct link on the localized page (visible for logged in contributors).
I think the translation module described and discussed in bug 398355 meets this need. When you update from the module, there is a diff that shows you stuff you need to translate. Maybe there should be a way to access this diff without having to edit the page, though. I can refine this next week.
ready for testing.
My only concern is that the link "update from it" is a bit unclear as to what will happen. It almost sounds like it could remove the "outdated" status without confirmation. Perhaps: "See changes and update this translation from it" Again, it should be a dynvar so we can localize it.