The labels of base fields that have overrides cannot be translated via UI. This makes it impossible to translate an entity form which shows some widgets of base fields; .e.g. I ran into this by not being able to translate "Authored by" or "Created on" on a node form.
* Make it translatable via the translation pages of their entity bundles, e.g. /admin/structure/types/manage/page/translate
* Finish patch.
User interface changes
* Some new translation options are available :-)
Data model changes