I don't cover Subway very much back in the States. Frankly, it isn't my favorite place for a quick sandwich. But there is no denying Subway's global presence. Here in Dubai you will find ordering your sandwich and the resulting assembly process to be familiar - it's identical to the way it is everywhere else. Even the topping and sauce choices are the same. For instance, I thought they wouldn't have honey mustard, but there it was, sitting in its little squirt bottle ready to go.
Above you can see some regional specialties, largely to cater to the Indian and Asian populations. Chicken Tikka and Chicken Teriyaki subs and a couple extra veggie choices. Of course at Subway ANY sandwich can be a veggie sandwich so that's probably what adds to the popularity.