Upgrading your programs from AWT Applicet to Swing JApplicet is much the same as for upgrading from Applet to JApplet: remember the getContentPane() thing. For the rest the API is unchanged.
To avoid having duplicates for helper classes like Browser and ParameterParser, we introduced an interface be.arci.applet.Framework, that is implemented by both Applicet and JApplicet. As a consequence, method signatures for the named classes and their subclasses have changed, to refer Framework instead of Applicet; remember to update your own subclasses, if any.
Also, we decided to make I18NDelegate an external class instead of an inner class of Applicet. We do not think this will have any impact on your code.