Change the OK Cancel string in JOptionPane

Looks like instead of JOptionPane.showConfirmDialog you are going to have to use JOptionPane.showOptionDialog, which lets you supply your own texts as an array.

Try the following:

JOptionPane.showOptionDialog(null, 
        "Do you like this answer?", 
        "Feedback", 
        JOptionPane.OK_CANCEL_OPTION, 
        JOptionPane.INFORMATION_MESSAGE, 
        null, 
        new String[]{"Yes I do", "No I don't"}, // this is the array
        "default");

Look at the javadocs in the detailed class description part:
You aren't limited to this set of option buttons. You can provide any buttons you want using the options parameter.
What (options) is also described there. Anyway the default texts (i.e. OK/Cancel) are usually based on the computer locale, but for custom labels use the method described in the javadocs.