A set of naval flags is larger and different to the international code flags. Some are the same visually but have different meanings. The code pennant just indicates that what follows should be read as international code. International code is used in conjunction with the international code of signals book. Although the official languages of the sea are English and French, (only the French use the latter) the code book can be in any language under the sun. Alpha Bravo Charlie in an English code book will have exactly the same meaning in any other language book. So if the other guy doesn't understand your language it's possible to communicate and understand each other's messages. Ie it's truly an international code. Military comms are totally different say between NATO navies and eastern block navies. Signals don't have to be sent only by flags. They can be spoken, morse (visual, sound or radio) or semaphore. In fact any method of transmission can be used but the items sent are letters and numbers taken from the code book.
Jerry.