In japanese, "Save", "Don't Save" and "Cancel" buttons in the "Unsaved Changes" dialog will be garbled (these button capton in the latest japanese language pack is empty).
Please fix these button (encoding bug?), use standard button, or use standard message dialog (e.g. "Click Yes to save the image and close it, No to discard the unsaved changes, or Cancel to go back to Paint.NET.". but this must remove the preview image...)