I am working with Ext.ux.form.ItemSelector. When I drag one or multiple items from one list to another special tooltip appears. How can I change / customize / localize this message?
The tip is controlled by Ext.dd.StatusProxy. You'll want to extend this to create your customized tip and then override the DragSource on your control to use your StatusProxy.
Alternatively if you want these changes everywhere you can just override the functionality in Ext.dd.StatusProxy itself.