"Your dog is dirty. Where did it go?"
"Your dog is dirty. Where has it been?" Is more natural. Unless the meaning of the sentence is "I was about to clean your dog because it's dirty, but where did it go?" (because it ran away). I assume it means the dog has been somewhere doing something to become dirty and the speaker is making that observation, in which case my version is more natural.
Thanks for help me suss this sentence. I couldn't for the life of me figure why they put the 了 in this sentence because I have never heard a native speaker use it when asking where someone is. Looking at it from this perspective, the Chinese prompt makes more sense.
Now if Duo could just hire some native English speakers to iron out the wrinkles in their translations, this course would be great.
Actually, although I didn't understand the "where did it go" half of the sentence at first, now that I've read Andrew's explanation above, I can totally imagine an American saying this, with a few slight changes in inflection: "Your dog is really dirty. OMG, where did he GO?"
I can see how it might sound odd to the non-American ear - as I said, I didn't understand it at first glance either, and I'm American - but I do believe this is something an American would be likely to say spontaneously. And, as we know, DL is US-based. So, this translation isn't COMPLETELY batty. Only somewhat. :-)