assertEquals("ja", languageHelper.getSupportedLanguage("ja"));
        assertEquals("en", languageHelper.getSupportedLanguage("en"));
        assertEquals("zh", languageHelper.getSupportedLanguage("zh"));
        assertEquals("ko", languageHelper.getSupportedLanguage("ko"));
    }

    public void test_getSupportedLanguage_unsupported() {
        assertNull(languageHelper.getSupportedLanguage("fr"));

     *
     * @param doc The document to update.
     */
    public void updateDocument(final Map<String, Object> doc) {
        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        String language = getSupportedLanguage(DocumentUtil.getValue(doc, fessConfig.getIndexFieldLang(), String.class));
        if (language == null) {
            for (final String f : langFields) {
                if (doc.containsKey(f)) {