improvement suggestion: real-world translations
I think it's good to have the real world translations, but I'm not sure whether it's good to see the same sentence I just translated as translated by someone else and then rate it.
If the other translation I see is great - then I might be able to see where I was wrong, but a lot of the translations are at the outer edges of what I can do at the time - so correcting someone else, with only having patchy knowledge myself, I am not quite sure what to say.
Two possible ways to improve:
a) provide a 4th option: can't say... For when I can't really say, whether the alternative translation is poor/ok/great...
b) I'm not sure whether duolingo tries to judge the difficulty of the sentence to be translated - IF you do, then I think it would be better to provide a sentence to translate that is slightly above par for my current skills -- but then to ask me to give feedback on a translation for a sentence that is 'below my current par'. This would obviously require that you start real-world translations at about the same time as is done now, but only start with evaluating other people's translations - a few stages later, when your skills have improved further. (i.e. start translating 'A1' level sentences early on - but only start evaluating others 'A1' level translations, when your own level is 'A2').
I think this a smart way to do things, since we are often unsure about our translations. I am at a level in German where I often get idiomatic expressions. I translate once myself and then ask my German boyfriend for feedback when I feel it is off. In some cases, NOT ONE of the translated sentences I have to judge is good, and I have to completely re-edit mine. If I did not have local feedback, the results would be translations about as bad as a machine could do.