NSPersonNameComponentsOrder.swift

import Foundation

private extension NSPersonNameComponentsFormatter {

    static let nameDefaultsByLocale: [String: AnyObject] = {
        let bundle = NSBundle(forClass: NSPersonNameComponentsFormatter.self)
        guard let url = bundle.URLForResource("NSPersonNameComponentsFormatterDefaults", withExtension: "plist"),
            let dict = NSDictionary(contentsOfURL: url) as? [String: AnyObject] else { return [:] }
        return dict["localeInfo"] as! [String: AnyObject]
    }()

    static func supportedNameDefaults(from locale: NSLocale) -> [String: AnyObject] {
        let preferredLocalization = NSBundle.preferredLocalizationsFromArray(Array(nameDefaultsByLocale.keys), forPreferences: [ locale.localeIdentifier ])
        return nameDefaultsByLocale[preferredLocalization[0]] as! [String: AnyObject]
    }

}

extension NSPersonNameComponentsFormatter {

    enum Order: Int {
        // "unset" is 0
        case givenNameFirst = 1, familyNameFirst
    }

    static func userPreferredOrder(for locale: NSLocale = .currentLocale()) -> Order {
        if let order = Order(rawValue: NSUserDefaults.standardUserDefaults().integerForKey("NSPersonNameDefaultDisplayNameOrder")) {
            return order
        } else if let order = (supportedNameDefaults(from: locale)["nameOrder"] as? Int).flatMap(Order.init) {
            return order
        } else {
            return .givenNameFirst
        }
    }

}

NSPersonNameComponentsFormatter.userPreferredOrder(for: .init(localeIdentifier: "en_US"))
NSPersonNameComponentsFormatter.userPreferredOrder()

// https://github.com/apple/swift/blob/swift-2.3-branch/stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift
NSPersonNameComponentsFormatter.userPreferredOrder(for: .init(localeIdentifier: "ja_JP"))
withOverriddenNSLocaleCurrentLocale("ja_JP") {
    NSPersonNameComponentsFormatter.userPreferredOrder()
}