We tried two japanese NLS_LANGUAGE settings :

JAPANESE_JAPAN.AL24UTFFSS and JAPANESE_JAPAN.JA16SJIS (Shift-J's).

I can't remember which one worked. It's been more than 2 years. But you can try both. Also we had Japanese Windows System to view Japanese characters. I'm not sure if just Japanese fonts would help. The underlying data in the database does not change. It's just how you view it.

It was important that the character set setting portion of this parameter (e.g. AL24UTFFSS) be the same as that defined during the creation of the database. What needs to change is the LANGUAGE and TERRITORY settings, depending on the data being accessed.