One thing I can remember is, with regards to oracle if you need multi-language support (i.e internationalization), one should use nvarchar instead of varchar.
The compatibilty depends on your JDBC driver. May be some else can enlighten us more.
Hey Pradip and ak pillai please go through this links, as I have worked with small internationalization assignement; I have gone through most of these problems. Onkly thing is that it was in core java/servlets/xml/xslt