Here's the scenario: we are supporting multiple languages with our iOS app. Our translations are done online with POEditor. As the xliff format supports localizations spread accross multiple localization files as well as plists (and even storyboards), it seemed like the logical choice for us.
So we exported the languages via Xcodes export option which can be found in the menu (Editor -> Export for localization, once the target is selected). After translation, we download the updated xliff files from POEditor.
These updated xliff files might contain new keys and text, as we assumed that they have to be added in POEditor first. This way, they will be added to the Xcode project once they are imported back again.
However, this does not work as expected. Once we import an xliff manually, the diff dialog will appear, warning us that the keys are not yet in the project, which makes sense as they are new. Clicking import works, however, new keys are not added.
Even if we add the keys manually, they will disappear once import is done instead of being updated.
Same is true for command line import, xcodebuild -importLocalizations -localizationPath PATH. Console reports: Key not found in the project (Key: "our_key")
My question would be: why is not possible to add new translations to our project via xliff that were only added in POEditor? Are we doing it wrong?
Edit
As it seems the single source of truth is Xcode and the development language. If new keys are available in localizable files of the dev language and the source text matches, all other languages will be added, even if keys are missing.
Still it seems to me Xcode is trying to be more clever than it should be...