LocaleUtils.java

package org.edx.mobile.util;

import android.support.annotation.NonNull;

import java.util.Locale;

public class LocaleUtils {

    public static String getCountryNameFromCode(@NonNull String countryCode) throws InvalidLocaleException {
        final String uppercaseRegion = countryCode.toUpperCase(Locale.ROOT);
        if (!isValidBcp47Alpha(uppercaseRegion, 2, 2)) {
            throw new InvalidLocaleException("Invalid region: " + countryCode);
        }
        return new Locale("", countryCode).getDisplayCountry();
    }

    public static String getLanguageNameFromCode(@NonNull String languageCode) throws InvalidLocaleException {
        final String lowercaseLanguage = languageCode.toLowerCase(Locale.ROOT);
        if (!isValidBcp47Alpha(lowercaseLanguage, 2, 3)) {
            throw new InvalidLocaleException("Invalid language: " + languageCode);
        }
        return new Locale(languageCode).getDisplayLanguage();
    }


    // Copied from Locale.Builder in API 21
    private static boolean isValidBcp47Alpha(String string, int lowerBound, int upperBound) {
        final int length = string.length();
        if (length < lowerBound || length > upperBound) {
            return false;
        }
        for (int i = 0; i < length; ++i) {
            final char character = string.charAt(i);
            if (!(character >= 'a' && character <= 'z' ||
                    character >= 'A' && character <= 'Z')) {
                return false;
            }
        }

        return true;
    }
}