In iOS 10 Apple added a new dedicated setting for Temperature Unit in the Settings.app under General > Language & Region > Temperature Unit . It lets you switch your preferred unit between Fahrenheit and Celsius:
Sadly Apple did not provide a public API for third party apps. Here is how you can access this preference in your app:
1- You first need to expose the NSLocaleTemperatureUnit NSLocaleKey:
FOUNDATION_EXPORT NSLocaleKey const NSLocaleTemperatureUnit;
2- You can now print the temperature unit. The value is one of these 2 strings: ‘Celsius’ or ‘Fahrenheit’.
NSLog(@"NSLocaleTemperatureUnit value: %@", [[NSLocale currentLocale] objectForKey:NSLocaleTemperatureUnit]);