if (lang == null) {
return new LowerCaseFilter(tokenStream);
} else if (lang.equalsIgnoreCase("greek")) {
return new GreekLowerCaseFilter(tokenStream);
} else if (lang.equalsIgnoreCase("irish")) {
return new IrishLowerCaseFilter(tokenStream);
} else if (lang.equalsIgnoreCase("turkish")) {
return new TurkishLowerCaseFilter(tokenStream);
} else {
throw new ElasticsearchIllegalArgumentException("language [" + lang + "] not support for lower case");
}