You'll need to change the default locale of your entire operating system to see how that affects the applet. In Windows you have to use the Control Panel's Regional Settings option to change the operating system's locale information. Of course, a normal user's information will already be set correctly. Only a developer will want to change the locale setting often. Windows will ask you to restart, but I have found you can ignore the restart prompt and simply restart the Web browser.
Many operating systems support the notion of resources.
Resources are files that contain strings and other items you might want to change depending on the default language or other constraints. For example, a Windows resource file contains the text it will display in menus, dialog boxes, and other messages. Java also handles the idea of a resource, although it does so in a different way from most other systems. For example, with Windows, resources appear in an executable file. Because ResourceBundle is an abstract class, the class you derive from it must provide the code for the handleGetObject and getKeys methods.