Most J2ME apps are designed for a specific language, so I18N is not a big issue. But for applications that require dynamic language swtiches, you would have implement your own "Resource bundle" of some sort. It is not very hard. My book does not cover this. But Vartan Piroumian's "Wireless J2ME Platform Programming" has an excellent chapter on this.
Also, the Sun 2ME blueprint application demonstrates how to develop the same app that runs in both english and japanese environments. The J2ME blueprint application is available from here:
http://java.sun.com/blueprints/wireless/ For an introduction to the blueprint application, check out my article:
http://www.enterprisej2me.com/pages/yuan/articles/sun-06202003.html