The translatability of entity changed timestamps provided by the ChangedItem field type was broken and is fixed now. As a consequence EntityChangedInterface::getChangedTime() now returns the changed timestamp of the translation on which this method is invoked.
But for use-cases that require the latest change timestamp of an entity regardless which translations has been edited, a new method called EntityChangedInterface::getChangedTimeAcrossTranslations() is introduced.
Some background information about why the translatability of the ChangedItem field type was broken:
Before the fix the ChangedItem field type that is used to realize such changed timestamps always set the timestamp to REQUEST_TIME on ChangedItem::preSave(), which seemed to be ok. But the nature of the entity storage is that it always saves all translations of an entity, regardless of the translation you call save() on. So what really happened was that the timestamp of the latest change to one translation of an entity got erroneously synchronized and saved across all translations! Therefor instances of ChangedItem field types were not translatable at all!
