Here is a good article on howto customize and configure portlets for internationalisation, use of locale, etc...

http://developers.sun.com/portalserver/reference/techart/i18n-portlets.html

out of 3 portals I have worked on, 2 were with 3 langages :
Flemish, French, German
French, English, Spanish

Hope this good practice article will be helpfull for the one that need to use several locales in portal...