IPhone – What are the implications of “Select Your Country or Region”

Is there maybe an AppleLocale key in ~/Library/Preferences/ByHost/.GlobalPreferences.*.plist? That would override the key in ~/Library/Preferences/.GlobalPreferences.plist.

This Apple support article explains that a valid payment method is always required when changing regions.

When you change the country or region of an existing Apple ID, you must provide a payment method and update your billing options. If you want to remove your payment method after you change the country or region, you can change your payment information to None.

You may be able to set up a new Apple ID for a different region without entering credit card information, but any apps purchased (whether free or not) with that Apple ID would require that Apple ID be signed in to get updates.

To create a new account without a payment method, go to the App Store, iBooks Store or iTunes Store on your device. Tap Get on any free item and follow the steps for setting up a new account. When prompted for a payment method, None should be on the list. If it's not, you must enter a payment method.