This is a most! We need a way to edit approved translations, in case we detect an error after approving. Of course we're suppose to review everything before approving, but sometimes it happens that we realize there was a better word than the one used in the translation or maybe we detect a typo, but it's impossible to fix it because fields are uneditable once approved...
I think if you allow this for managers, it would improve overall quality. You could also allow translators to edit their own translations, after they are sent in order to fix possible errors before.
But, for this exceptional situations you can use the "report bug" link. Just the way you use it to report inaccuracies in gray fields (pre-approved ones). I've done it this way, of course trying to keep this practice to a minimum, in order not to overload the admins with it.