public static String getCurrentLanguage() {
        return calculateLanguage(getCurrentLocale());
    }
Gets ISO 639-1 Language Code from current Locale so 'pt_BR' becomes 'pt'.

@return the ISO 639-1 Language Code
@see <a href="https://www.w3schools.com/tags/ref_language_codes.asp">HTML Language Code Reference</a>
primefaces/src/main/java/org/primefaces/util/LocaleUtils.java