Changing the locale in a Swift playground

Locale.playground

import UIKit

extension NSLocale {
    class func currentLocale() -> NSLocale {
        return NSLocale.localeWithLocaleIdentifier("en_GB");
    }
}

NSLocale.currentLocale().localeIdentifier

let numberFormatter = NSNumberFormatter()
numberFormatter.numberStyle = NSNumberFormatterStyle.CurrencyStyle
numberFormatter.stringFromNumber(10)

Swift 4 version:

extension Locale {
    static var current : Locale { return Locale.init(identifier: "fr_FR") }
}