There's no standard way to set the default language; this is specific to each JVM implementation and host platform. For most Windows JVMs, the procedure for doing this is the one you already described: changing the locale in the Control Panel settings.
If this isn't appropriate for what you need to do, then you'll just have to use the command-line option you mentioned. Some JVMs allow you to specify command-line options in an environment variable, or to read system properties from a file, so you may want to see if those approaches apply to your JVM.
unfortunately i am not able to use vm arguments. So have come up with a way to keep the properties on a server file which the user can update which will in turn change the language to japanese. A bit of a hack, but no other way i have found works.
Ben
With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.