There are always huge discussions about this, and I never understand why developers and companies go for the complex way.
The language selected by the user, means the language he/she wants to see always in his/her phone. They don’t intend to have apps in a different language than others or the system.
The choice is very straight forward: Use Locale (to get the language the user selected as preferred), or make your best to piss them off showing them information in a language they already said they don’t want to see things in.
To get the country code use:
Locale.getDefault().getCountry();