我检查了我的Android 4.1.2设备上的Locale方法，结果是:

Locale.getDefault().getLanguage()       ---> en      
Locale.getDefault().getISO3Language()   ---> eng 
Locale.getDefault().getCountry()        ---> US 
Locale.getDefault().getISO3Country()    ---> USA 
Locale.getDefault().getDisplayCountry() ---> United States 
Locale.getDefault().getDisplayName()    ---> English (United States) 
Locale.getDefault().toString()          ---> en_US
Locale.getDefault().getDisplayLanguage()---> English
Locale.getDefault().toLanguageTag()     ---> en-US

public void GetDefaultLanguage( ) {
    try {
        String langue = Locale.getDefault().toString(); //        ---> en_US
        /*
        Log.i("TAG", Locale.getDefault().getLanguage() ); //       ---> en
        Log.i("TAG", Locale.getDefault().getISO3Language()  ); //  ---> eng
        Log.i("TAG", Locale.getDefault().getCountry()  ); //       ---> US
        Log.i("TAG", Locale.getDefault().getISO3Country()  ); //   ---> USA
        Log.i("TAG", Locale.getDefault().getDisplayCountry() ); // ---> United States
        Log.i("TAG", Locale.getDefault().getDisplayName() ); //    ---> English (United States)
        Log.i("TAG", Locale.getDefault().toString()   ); //        ---> en_US
        Log.i("TAG", Locale.getDefault().getDisplayLanguage() ); //---> English 
        */

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            langue = Locale.getDefault().toLanguageTag(); //     ---> en-US
            url_Api = getUrlMicrosoftLearn(langue);
            Log.i("TAG", url_Api );
            Log.i("TAG", langue );
        }else{
            langue = langue.replace("_","-"); //     ---> en-US
            url_Api = getUrlMicrosoftLearn(langue);
            Log.i("TAG", url_Api );
            Log.i("TAG", langue );
        }
    }catch (Exception ex) {
        Log.i("TAG", "Exception:GetDefaultLanguage()", ex);
    }
}

public String getUrlMicrosoftLearn(String langue) {
    return "https://learn.microsoft.com/"+langue+"/learn";
}

以上答案没有区分简体中文和繁体中文。 Locale.getDefault(). tostring()工作，返回“zh_CN”，“zh_TW”，“en_US”等。

参考:https://developer.android.com/reference/java/util/Locale.html, ISO 639-1是旧的。

下面是获取设备国家的代码。兼容所有版本的android甚至奥利奥。

解决方案:如果用户没有sim卡，那么在手机设置或当前语言选择时获取他所使用的国家。

public static String getDeviceCountry(Context context) {
    String deviceCountryCode = null;

    final TelephonyManager tm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);

        if(tm != null) {
            deviceCountryCode = tm.getNetworkCountryIso();
        }

    if (deviceCountryCode != null && deviceCountryCode.length() <=3) {
        deviceCountryCode = deviceCountryCode.toUpperCase();
    }
    else {
        deviceCountryCode = ConfigurationCompat.getLocales(Resources.getSystem().getConfiguration()).get(0).getCountry().toUpperCase();
    }

  //  Log.d("countryCode","  : " + deviceCountryCode );
    return deviceCountryCode;
}

public class LocalUtils {

    private static final String LANGUAGE_CODE_ENGLISH = "en";


    // returns application language eg: en || fa ...
    public static String getAppLanguage() {
        return Locale.getDefault().getLanguage();
    }

    // returns device language eg: en || fa ...
    public static String getDeviceLanguage() {
        return ConfigurationCompat.getLocales(Resources.getSystem().getConfiguration()).get(0).getLanguage();
    }

    public static boolean isDeviceEnglish() {
        return getDeviceLanguage().equals(new Locale(LANGUAGE_CODE_ENGLISH).getLanguage());
    }

    public static boolean isAppEnglish() {
        return getAppLanguage().equals(new Locale(LANGUAGE_CODE_ENGLISH).getLanguage());
    }


}

Log.i("AppLanguage: ",     LocalUtils.getAppLanguage());
Log.i("DeviceLanguage: ",  LocalUtils.getDeviceLanguage());
Log.i("isDeviceEnglish: ", String.valueOf(LocalUtils.isDeviceEnglish()));
Log.i("isAppEnglish: ",    String.valueOf(LocalUtils.isAppEnglish()));

如果API级别为24或以上，则使用LocaleList.getDefault().get(0).getLanguage() 否则使用Locale.getDefault.getLanguage()

private fun getSystemLocale() = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
    LocaleList.getDefault().get(0).language
} else {
    Locale.getDefault().language
}

参考:https://developer.android.com/guide/topics/resources/multilingual-support