I also have the same issue in jBoss4.
Two struts web application runs on one jboss node in my hosted machine (system local is en_US). But, changing local from sv_SE to en_GB does not reflect in the UI.
My default properties file also in English.
waitting for a answer.
Apologies for the time it took me to respond!
From a quick test I did, changing the language in GateIn correctly updates the internationalized parts of the JSF portlet, when the "en" properties file does not include the locale portion.
Basically I built the GateIn Quickstart for JSF2 and tried it.
Once difference I can see is that the quickstart doesn't set the supported locales in portlet.xml, so not sure if that is causing an issue or not.