I have a simple experiment for doing internationalization. In this example I'm using css content properties to not reload the app when a lang changes. It works pretty nice but I'm not sure about the performance yet.
Check the example working at http://elmasse.gaver.nl/projects/bundle-css
Or see the code from github repo at https://github.com/elmasse/Ext.i18n....ee/css-content
As I said, this is an experiment. Maybe it can be ported to ExtJS so the impact of adding more dom elements is not as important as in mobile.