In language file(s) there is a line: <str id="nextmedia.filedesc" rdid="install packs (.pak*)"/>. There is an attribute "rdid". Counterpart for attribute "id" is usually "txt", but not in this case. "nextmedia.filedesc" is used in src\lib\com\izforge\izpack\panels\NextMediaFileFilter.java. LocaleDatabase which is used in this class will load "id"s and "txt"s. DTD will talk also about "id" and "txt". I stamped this as a bug although this won't prevent execution but it looks like an error.