Hey, thank you for your comment.

"With systemwide support for in-app language selectors, you no longer need to provide a way to select languages within your app if you support iOS 13 or macOS Catalina or later. "

It is not declaration of forbidding the use of any other localization methods, just a suggestion that "you can do it our suggested way, no longer needed for other methods". It seems not to be breaking any of the Apple's rules.

The only part in my tutorial missing is monitoring the language set via Settings > "App name" > Language and not displaying the updated language change in app. But you can do it by monitoring the AppleLanguages UserDefaults key. Just some custom additional logic need to be added.

In the end, you would have fully supported localization feature in both system's and app's perspective. You change the language in Settings? No problem, the app would display the change. You change the language inside the app? No problem, the system would be informed on the language change (this is already provided in the tutorial). As long as you provide a smooth experience, it is all good.

P.S. I have not published any apps with this localization method, however, I have seen other apps having similar implementations and having no problems.