Tested with 5.0u2 b04.
Trying to show exception messages by following testcase in Japanese environment, English message is shown instead of Japanese.
http://jeeves.sfbay/cgi-bin/cvsweb/rowset2.0/test/qcts/src/tests/rowsets/i18n/cachedrowset/Attic/CachedRowSet1.java

Looking into following sourcecode,
src/share/classes/com/sun/rowset/JdbcRowSetResourceBundle.java

        String suffix = locale.getCountry();
        if(!suffix.equals("") && !suffix.equals("US")) {
           // Load appropriate bundle according to country
            try {
               propResBundle = new PropertyResourceBundle(
                        Thread.currentThread().getContextClassLoader().getResour
ceAsStream(
                          PATH+UNDERSCORE+suffix+DOT+PROPERTIES));

this results in seeking for *_JP.properties instead of *_ja.properties.
ResourceBundle should be loaded appropriately with ResourceBundle.getBundle().
###@###.### 2004-12-28 10:53:58 GMT