Swimming costume is fairly common in the UK. It should accept swimsuit too.
Is it? I'm Irish and our cultures are quite intertwined between various media and I've never heard that before. I'll defer to you on it though! In any event, I reckon "swimsuit" should still be accepted as a more universally used translation, even if I wouldn't necessarily say it myself.
Yep, we really do say "swimming costume", or even "cozzie" for short. Not really sure how to spell that, it's very much a spoken-English thing. I think it's a bit old-fashioned now, though, and most English people would say "swimsuit". Interestingly that's what I typed, and Duo thought it should be "swim suit" with a space, but you guys seem to agree on the one-word spelling.
Oh it definitely should be, I'm sure I saw an American asking a similar question a few weeks back about the same word.
It now DOES not accept swimming costume, which is the only term I have ever used in the UK.
I think it should accept swimming costume as that is a valid term that is still in use in the UK