import java.util.*;
import javax.swing.*;

public class OptionPaneTest {

    public OptionPaneTest(String msg) {
        // If your operating system is English, set to any non-English locale.
         Locale.setDefault(Locale.FRENCH);
        JComponent.setDefaultLocale(Locale.getDefault());
        System.out.println(Locale.getDefault());
        System.out.println(JComponent.getDefaultLocale());
        //JOptionPane.showConfirmDialog(null, "Are you sure?");
        //JOptionPane.showConfirmDialog(null, "Êtes-vous sûr?");
        //JOptionPane.showConfirmDialog(null, "你確定?");
        JOptionPane.showConfirmDialog(null, msg);

    }

    static public void main(String args[]) {
        SwingUtilities.invokeLater(() -> new OptionPaneTest("Êtes-vous sûr? 你確定?"));
        //SwingUtilities.invokeLater(() -> new OptionPaneTest("你確定?"));
    }
}