> On the one hand, this is linguistically correct… if we were speaking Spanish.
I don't see many English words ending in X, so I doubt it's linguistically correct in English either.
Normally you just borrow the word as closely as possible, maybe trying to make it easier to pronounce (see any word the Japanese borrow from English), but here people that didn't speak Spanish, but apparently knew a little bit took over.
English corrupts a lot of stuff it borrows, the examples which come to mind are when people try to be fancy. See also "chai tea", the difference between beef and cow. Also corrupts itself spontaneously, what with all the "u"s in British English or how many "i"s there are in aluminium.
Ok, but this isn't a Portuguese/Spanish/French word that was borrowed into English that naturally got a final X because it suited English better.
I didn't say there are no words ending in X, but it isn't common and it's not a way to help borrow words from other languages, nor is the X also borrowed.
I don't see many English words ending in X, so I doubt it's linguistically correct in English either. Normally you just borrow the word as closely as possible, maybe trying to make it easier to pronounce (see any word the Japanese borrow from English), but here people that didn't speak Spanish, but apparently knew a little bit took over.