Nayrouz NZ:
Hitoshi Ozawa plz can you explain more what do u mean by "customize the source code so it's internationalized"??
Thanks.
IMHO It simply means that you would have to customize your custom plugin portlet and include the following:
1) Language property files, one for English and the other for French for static content like button labels, title, heading, field labels etc.
2) If you allow the User to create some content in your portlet and want to display that in both French and English then you would have to modify your code to give the User option to enter French as well as English content, just like liferay does in web-content portlet.