I couldn't find anything about this feature, and I think it would be useful. If I'm editing a page that is enclosed in <translate> tags, and in one part I am making significant content changes, and in another part, I am only fixing typos or grammar, it would be nice to be able to mark the minor edits as not needing a new translation, as typo or grammar fixes probably won't affect the translation and will just waste translators' time.
For example, it could be done by placing <minoredit> tags around the grammar fix, which the Translate Extension then deletes from the source, and then it makes sure to not display the edited unit as needing translating (unless, of course, it still has major edits that need translating from prior revisions or from a different part of the unit).