So....does the French sentence clearly only refer to outer space? Because then, as others have said, it has to be "into space". And it can be "Men" or "The men", depending on if you are speaking generally or about some particular guys.
But if it can also refer to some physical space that some men entered, it still needs to be "into", not "in", but the article remains - i.e., "into the space.". And then it would most likely be "The men", since stating that "men" in general have entered that specific space (under the stairs, between the houses, whatever) seems a bit silly.
The other thing that occurs to me is that "...have gone in the space" rather sounds as if they disappeared, but it's kind of ambiguous, so if that's what was meant, it would be better to say "disappeared".
It means that sometimes there are not enough hours in the day, or eyes to read all of the suggestions on Duolingo - it is a mistake. French use many more articles than we do - so sometimes a perfectly good sentence in French is incomprehensible in English because there is an extra "the". Men have gone into space. is a nice English sentence. But getting from the French to the English requires that you know that this is one of those times when we don't use the article AND that because there is direction of movement, we use INTO rather than IN. But if you translate literally, word for word - you can come up with strange things that go bump in the night. Welcome to learning languages. Take a deep breath, smile, and be assured that you are not crazy. Go onto the next sentence. Overall Duolingo corrects itself, and in five years it will be a lot better than it is today. Bye now.
Hi salihua, I agree completely with you. My only worry is that I might be learning to speak 'Duolingo French' and by the time the online crowd have perfected DL it will be too late for me and I will only be able to communicate with those who have learnt French on this site ;) Deep breath, deep breath......1/oct/14
Now that IS a thought! A secret language for the on-line community. Perhaps it would be a combination of all the different languages offered by Duolingo. Much better than Esperanto. You would just switch languages at each sentence and not tell anyone which one you were speaking next. As a bonus, you would bring remnants of grammar from each language into the next. You really have something there!