INSERT INTO `XS_flags` (`flag_id`, `flag_name`, `flag_image`) VALUES (1, 'Curacao', 'curacao.png');
what's the flag_id though?
You can omit the id, so you won't be bothered to look at the latest available id...
Use this way for each flag:
INSERT INTO `phpbb_flags` (`flag_name`, `flag_image`) VALUES ('Curacao', 'curacao.png');
Remember to change your table prefix if needed.