This one is one of my pet peeves even outside of Apple Pay. My personal opinion is that almost all iconography is just reinventing the wheel. We already have a widely-accepted iconographic vocabulary already understood by a billion people: Chinese characters. The fact that English speakers can't read it is immaterial, because English speakers already can't read the icons we're already using. Using Chinese iconography in all languages will dramatically increase the legibility of the icons we use in apps.

(Or, we could just put regular text under the icon...)