Someone told this story at a wedding I attended a few years ago.
There was a time not so long ago that people would only have one good outfit that would be used for special occasions. Girls would add some variety by adding a bow here, or maybe a scarf, but close friends would would sometimes add variety by swapping dresses. Mary was going to a big dance one night, and she borrowed Brigid's yellow dress. She was asked to dance by a boy that she didn't recognize, and as they danced she asked him if they had danced before - he replied "I don't think so, but I've danced with your dress!"
I find this English to be odd. Could "dress" mean "attire?" I know some languages can use the same word for the particular garment ("a dress") and the way a person is dressed (e.g. "casual dress"). Is that what is happening here, or do we have six people wearing the same garment?
I guess it could be six people passing it around and wearing it one at a time. It's not "We are wearing the dress."
A lot of Duo sentences are odd to begin with, but I think this one comes fairly early on in the Irish lessons, before plurals are taught, but where we're learning to use verb conjugations. Think of it as a uniform of some kind, like in a girls' school, or maybe a strange religious cult. "When we enter these doors, we wear the dress."
Sometimes, it's the really odd sentences that prove you understand the grammar and vocabulary. The first time I attempted to read a "Harry Potter" novel, I attempted to read it in Spanish.
At the time, I had thought my grasp of Spanish to be fairly good, but there was one sentence I kept reading and re-reading. I couldn't get past it. The sentence did not make any logical sense to me and I thought, "Surely, this must be an idiomatic expression with which I am not familiar."
Finally, I surrendered and took up an English copy of the book. Wouldn't you know, the cat actually WAS reading a map? I should have just trusted myself in the first place.
I think it's a metaphor. The dress is the planet, which we all 'wear' together, each person tasked with maintaining his or her portion of the 'fabric' to preserve the structural integrity of the overall 'thread' not just for the current 'wearers', but for future generations.
...Or Duolingo just has another odd sentence. Now that I think about it, I'm going with that.
I wonder do Duolingo get the computer to pick the verb, then pick the form at random from first person singular to third person plural and then pick at random an associated noun that goes with the verb so we end up getting nonsense like this.
Ever seen the play "Hair" ? The Tribe Supreme Trio: http://soulfuldetroit.com/showthread.php?2673-Supremes-Trio-Hair
"Caitheann siad an gúna." ---this image always comes to mind :)