LocaleUtils.java

public class LocaleUtil {
    private static Pattern pattern = Pattern.compile("^([a-z][a-z])(_([A-Z][A-Z]))?$");

    /**
     * Returns null if the string couldn't be parsed
     */
    public static Locale parseStringToLocale(String s) {
        Matcher matcher = pattern.matcher(s);

        if(!matcher.matches()) {
            throw new IllegalArgumentException("Could not parse locale")
        }

        String language = matcher.group(1);
        String country = matcher.group(3);

        if(country == null) {
            return new Locale(language);
        }

        return new Locale(language, country);
    }
}