If you were translating for someone who was very animated in their expression of disbelief, you might more liberally or colorfully translate this as, "Are you kidding me?", "You must be kidding", or a bit of weird slang, "Get outta town!", or "Shut up!"
If the person was very serious when saying this, it could mean, "Don't say that to me"
But generally, it would mean "You don't say"
More's the pity. I often wish we still had the separate 2nd-singular and 2nd-plural, so we didn't have to resort to "y'all" or "youse" or "you guys". :-)
"Thou" used to be our 2nd-singular-familiar, and "you" was 2nd-plural or 2nd-singular-formal, but that distinction started to decay at least three centuries ago, and we ultimately lost the "thou" form entirely. I guess we just decided to treat everybody with respect / formality?
I agree it should be "You don't say!" but I was afraid to put it because I just knew it wouldn't be accepted, so I tried to do what I thought might fly, and it did. However, what they accepted is less natural than what they should have accepted. Question: How do you know when they change it? I report lots of things, but I never get a reply.
I feel our input is important. Duolingo is amazing, and I realize it is nearly impossible to cover every possible answer, but there are times when translations are so unnatural or even wrong that I report it in an effort to help fix whatever problems there may be. It's only through our reporting that their attention will be drawn to it, so I look at it as being helpful.
I have Mexican friends on here doing the English program, and there have been times when they say that they thought they had something figured out (Who vs. Whom, for instance), and then the response made them question what they had learned, when in fact, they were correct.
My only concern is that there is no follow-up after I report something, or maybe I just don't know where to look for it. I may be missing something.
I as well fell into the trap. And I do want to post here and clutter this up because 16 other people agree yet Duolingo has done nothing to correct it.
I must say, I'm not as happy with Duolingo as I used to be. The font is so small for me when I use the website login. And now since the latest update, I can't use the phone app either because there is no skill button.
They have a number of expressions to cover those as well. If you are looking for a translation of "No me digas!" you should stick with the expression, "You don't say!" That's more an expression of amazement. "Really?" sounds more doubtful, more questioning . . . disbelief! But just as in English, there are lots of ways to convey a certain idea, Spanish is no different. You choose. But Duo isn't about whatever else can be substituted for an expression. Unfortunately, they caused a lot of confusion on this one by translating it literally instead of for the idiom it is.