For a better understanding of Masterpages and Fragments you may find some ideas here. It is the SAP LC Designer but the same concepts may help you. Forget about all the SAP related stuff...
I don't know if I understand well your need. but this small XDP have 2 different master pages, 1 to english part and other for language specific pages. You need some like this, but separated in differents XDP's to reuse it?