If a word is borrowed from another language and becomes common place, you can use the plural form of your language. Do you say “5 pizzas“ or “5 pizze“? A notable exception are Latin words, e.g. index -> indices (if you want oto sound well educated).

The japanese plural of “emoji“ would be “emoji“ (they have no plural form)

EDIT: I'm not saying it's wrong to use the native plural form, though!