I am posting this for comments:

Problem:
- Displaying the portal/portlets with the favorite user's language.
- How to determine the favorite language of a user compared to what is available.

Information:
- A user could define his preferences at different levels
1 - By the browser, this is convenient, a user can list the languages he prefers and order them.
2 - By the user profile, either by defining 1 favorite language or several ordered by preference
3 - By links on the website (so only 1 language at a time)
- A portlet defines the languages it supports, we can have a portal with different languages for portlets

From the JSR168 Specs:

PLT.11.1.8 Internationalization The portal/portlet-container decides what locale will be used for creating the response for a user. The portal/portlet-container may use information that the client sends with the request. For example the Accept-Language header along with other mechanisms described in the HTTP/1.1 specification. The getLocale method is provided in the PortletRequest interface to inform the portlet about the locale of user the portal/portletcontainer has chosen.

Solutions (proposals):
- If a user defines his favorite language in his profile or click on a link on the portal to define the language and if a portlet accepts it, it's all fine, we know what to use. In order of priority Link -> Profile -> Browser
- If the portlet only accept 1 language, we must choose it.
- Now the problem is when the portlet accept different languages but not the one chose on the portal, neither the favorite in the user preference.