JavaFX change locale language during application run time

Question

I'm using resource bundles to manage languages in my app. In my main class i have:

@Override
    public void start(Stage primaryStage) throws Exception{
        Locale.setDefault(new Locale("pl"));
        ResourceBundle bundle = ResourceBundle.getBundle("bundles.messages");
        Parent root = FXMLLoader.load(Gui.class.getResource("difficulty_choice_window.fxml"), bundle);

        Scene scene = new Scene(root);
        primaryStage.setTitle("SudokuGame");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

And setting language from this level, works perfectly fine, so i wanted to add a feature to change the language in the application's run time, hence i assigned this line, to a button that's suppoused to change the language:

Locale.setDefault(new Locale("en"));

As you might guess - it doesn't work. What would be the correct way to do it?