The "get" method can handle up to 4 parameters which is the usual number of parameters

Exemple :
$msg.get("key", ["12", "3"])

#set($list = ["12", "3"])
$msg.get("key", $list)

I left the normal (non-list) methods because they are more "user-friendly"

I believe the implementation can be improved a lot. For example you don't seem to be using the standard and defacto way in Java, which is to use the MessageFormat class... This means your implementation doesn"t support all the nice features of MessageFormat. See http://java.sun.com/j2se/1.4.2/docs/api/java/text/MessageFormat.html

Thanks
-Vincent

Added documentation to http://www.xwiki.org/xwiki/bin/view/DevGuide/InternationalizingApplications