User Role Editor WordPress plugin Japanese translation is added with v. 2.0.3 release at April 14th, 2010. Thanks to Technolog.jp for the help.
After 6 months of participation in WordPress plugins developement I still wonder how people from all over the World help each other in order to make their sweet blog platform better. Thanks to all current and future contributors!
One useful note: Please not be confused with usual WordPress language translation files naming scheme name-nn_NN.po, name-nn_NN.mo, where nn_NN – language code, e.g. it_It, es_Es, etc. Such scheme is valid not for all languages. For example for Japanese we must use just a ja as the language code.
So today, at April, 15, 2010 I had to rename ure-ja_JP.po and ure-ja_JP.mo files to ure-ja.po and ure-ja.mo. The source of information about WordPress specific language codes can be found here. I didn’t change plugin version and left it as 2.0.3 to not bother plugin users with plugin update requirement. If you downloaded URE 2.0.3 package yesterday, just rename Japanese language files according to the scheme above or download the latest installation package.
User Role Editor plugin description and download link are available at this page.

User Role Editor WordPress plugin German translation is updated with plugin v. 2.0.2 release at April 11th, 2010. Thanks to Peter for continued support.

To make new version of the plugin available to public faster I use on-line translators to update plugin language files. Of course, I understand, that easy accessible automated translation technologies (Google, Yahoo, other on-line services) are not good enough yet to replace a human in this field. So I include such on-line translated files into plugin’s package just as the starting point for some enthusiastic person to help me with real human translation. If you can help with my plugins translation to other languages, you are welcome! Left me your email via Contact form and I will send you my email address where you can send translation files.
I use Poedit software for work with translation files. If you have not experience in translation files creation/modification please read this article and related materials.

User Role Editor plugin is available for download here.