In your buttonActionPerformed() method, you set your resource variable to the resource bundle for English, but then don't do anything with it. I think you probably want to change the label on your JLabel control.
It this isn't clear why, just consider that the way the application is currently coded, you set the label on the JLabel control only when you create the application (in the initComponents() method).
Also, I see when you click the button you change from the default language to English. What is the default language? If it's English, you won't see any change anyway.
Finally, you should use import statements to import your javax.swing components, and not use the fully-qualified class name when referencing them in the code. The way you have it now makes it harder to read.