1) Switch to japanese locale
2) Run any (non-java) app, e.g. Notepad, switch to "Arial" font, and put some japanese text into it. You can see the text is properly rendered.
2) Run java-app which components use "Arial" font, and contain japanese text. You won't see the text rendered (the java font mapped to arial is not capable to do it).

It seems the fonts in java are not properly mapped to the OS fonts.

Also the API, GraphicsEnvironment.preferLocaleFonts(), doesn't seem to make any difference.

There doesn't seem to be a way how java programmer could fix this issue.

See the attached test app (TestFonts):
1) Run it when the japanse locale is set (it is a NetBeans project),
2) You can see that component using "Arial" font can't show the characters, while the one using "SansSerif" can.
3) If you run other non-java app (Notepad), it can show the text in "Arial" font.