Poe also understands BB8.
Luke needed an x-wing translator at first (and always? or did he not need it in ROTJ? I can’t remember)
Pretty sure he used it in ROTJ. I think we see it on screen.
Of course Rey worked in an outpost/spaceport thingy so you can assume she’s been exposed to all sorts of different languages, which I guess is why it doesn’t really bother me anyway.
I was about to say this before you said it yourself. It’s a non-issue.