First Day of Week setting does not apply without app restart

Originator:nikhil
Number:rdar://FB10193618 Date Originated:12/06/2022
Status:Open Resolved:No
Product:Foundation Product Version:16.0
Classification:ncorrect/Unexpected Behavior Reproducible:Yes
 
Issue: 

Changing the First day of week setting under Settings > General > Language & Region does not apply with an app restart. 

Steps to reproduce:

- Launch Calendar.app (or any other app using NSCalendar/Calendar in some way)
- Open Settings.app and then navigate to General > Language & Region and change the First Day of Week setting (eg. from Sunday to Monday in the Indian region) 
- Open Calendar.app again
- The UI isn’t updated to reflect the new setting 

Additionally, `Calendar.current` and `Calendar.autoupdatingCurrent` don’t have the latest value on `.firstWeekday` either. The correct/latest values are only available after the app is quit and launched again. 

Expected: 

- The value on `Calendar.current.firstWeekday` should update as soon as possible to reflect the user selected value. 
- Provided a new notification to observe this change (or optionally post the `UIApplication.significantTimeChangeNotification` notification)

Comments


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