public static Language from(String languageTag) {
        Objects.requireNonNull(languageTag, "languageTag cannot be null");
        Language language = fromLocale(LocaleFactory.fromLanguageTag(languageTag));
        if ( ! languageTag.equalsIgnoreCase("unknown") && language == Language.UNKNOWN)
            throw new IllegalArgumentException("Unknown language tag '" + languageTag + "'");
        return language;
    }
Returns the Language from a language tag

@param languageTag the language tag for which the <code>Language</code> to return, cannot be null
@return the Language instance
@throws IllegalArgumentException if the language tag is unknown
linguistics/src/main/java/com/yahoo/language/Language.java