Messages are stored in properties files which are located at the /metainfo/mesg directory of the classpath. Each module is associated with an unique name. In addition, the Locale is appended to the property file, too. For example, the message file of zk.jar for Germany messages is msgzk_de_DN.properties or msgzk_de.properties. Currently, zk.jar is only shipped with English and Chinese versions. You could add your own property files for different Locales by placing them at the /metainfo/mesg directory of the classpath.