The "international" version is in fact the same as the "english-only" one, regarding the localization support in the Limewire software itself.
The difference is only that the "international" version bundles an international version of Java.
But if you have already installed the international Java JRE from the Sun web site, you don't need the "international" installer of Limewire to work in Japanese.
Just download the "english-only" installer, and you'll get the same version of Limewire, supporting the same set of languages.
All localization issues are not in Limewire itself, but depend on your OS support for international fonts and keyboard input methods, and in the version of Java you have installed.

So, on Windows:

- install or update Java to the latest version (using the control panel, you'll update to the latest release of Java 1.4, but you can install the Java 1.5 JRE which is extremely stable, although it is still labeled by Sun as "Beta", only because it lacks some new features that are not fully tested, but that Limewire does not use; Java 1.5 is still in development by Sun, but all the Java 1.4 compatible API is already extremely stable and even better than in the Java JRE 1.4 implementation)

- then install Limewire's "english-only" installer. The installer is smaller because it does not ship Java (Java is detected and the JRE 1.4 is downloaded separately if it is not already installed on your system).

The "international installer" was needed on Windows only to help the most common basic users that don't know how to install Java on their system, and want something that will run immediately on their fresh new system.

For MacOS, OSX and Linux, a Java JRE must be installed prior to installing Limewire (but these users are generally less basic users, and know better how to manage their systems...

On MacOS, MacOSX, Apple bundles on its OS or on its MacOS online update service an excellent help to install a compliant Java JRE. But such active support is not done so well on Windows.

(Microsoft does not want to support Sun's Java, even if it has removed its own non-compliant Java implementation from Windows; things should change because Java development is so much important for enterprise applications on Windows today: look at the many IT jobs that DO require today a good knowledge of Java J2EE and Oracle, and compare it to the very few job offers that need .Net skills; the standard Sun's Java is a must on Windows and other systems, whatever Microsoft thinks and declares everywhere, and it is used in so many enterprise-critical missions that you can be confident it is extremely secure, unlike the now obsolete and very insecure Microsoft JavaVM).

Note: J2EE is a superset of the J2SE environment in Java. Limewire does not require the large J2EE (used in enterprise for N-Tier applications running on application servers), and just uses the basic J2SE edition running locally on your OS.