WP_Multilingual is a plugin that enables multilingual functionality, and it had stopped working since upgrading to WordPress 2.8. However, thanks to the generosity of its developer, we were able to get the alpha version back to life.

It's currently working without any noticeable issues.

The FCKEditor that was previously required is no longer necessary, so you can input using the beautiful WordPress interface, and the language switcher has been made into a widget, so it's not just usable, it also addresses some of the shortcomings that I thought were missing, which is great. There was no Japanese localization, so I quickly translated it and provided the language file.

If you are a WordPress user and are considering multilingual support, please give it a try.