Why are there so many faults? I am taking the French course which is a beta version. The percentage of faults in the German course is not much lower. Because my knowledge of German is very much better than of French I can judge how bad the mistakes are. For instance; "Sie sollen die Arbeit machen" is translated into "you should do the work". Not a bad phrase, but unhappily enough the translation of: "Sie SOLLTEN (with extra -t-) die Arbeit machen" The original phrase is to be translated into: "you have to do the work." I know enough German and English to dismiss the nonsense, but there are many out there who depend on the material Duolingo gives. I like the idea and the work invested, but the results make me sad.
@siebolt: EDIT: In my first answer I misread your complaint, sorry about that. 'Sie sollten...' is a polite reminder. But 'Sie sollen' ( 'Sie' meaning 'you') is indeed a stronger demand than 'you should' IF it comes directly from the person that gives you the 'order'. On the other hand, if our boss asked me to inform you that you should do some work for him, most naturally I'd say to you 'Sie sollen das Schreiben fertig machen'. In this case the meaning is more 'The boss asked you to...' than 'you have to' or 'you must'. In general, 'sollen' can be used in a whole bunch of different situations and the meaning depends on context. http://www.duden.de/rechtschreibung/sollen
@siebolt: no, I don't think so. 'sollen' is a quite tricky word since it can have so many different - and to some extend even contradictory - meanings: From a very strong moral obligation 'Du sollst nicht töten' to the expression of very uncertain knowledge 'sie sollen die Abgeordneten bestochen haben' ('corre voce que...')
@siebolt: No, it wouldn't be wrong at all. If your boss comes to you and says 'Sie sollen (gefälligst) arbeiten!', 'you must' or 'you have to' would be totally fine as a translation. The only point I want to make is that - as no additional context is provided - duolinguo's translations are also possible.
@siebolt: ;-) I wouldn't have believed the gossip anyways ;-) I totally understand that as a teacher in the Netherlands you put a lot of emphasis on the distinction between 'sollen' and 'zullen' as they are very tempting 'false friends'. I guess for English speakers the distinction between 'should' and 'sollen' isn't as important. And it wouldn't be right for duolinguo to dismiss correct translations. The examples I gave you are not handcrafted for very specific contexts but are used on a day by day basis in Germany. However, I agree that the three meanings you gave are probably the most common ones and duolinguo should ('sollte') certainly accept these. I don't consider 'you have to work' as the most natural translation of 'Sie sollen arbeiten' , however ('you ought to' or Fleur's 'you're supposed to...' are more natural in my opinion). But what appears most natural to us depends strongly on the context we implicitely construct when hearing the sentence.
I didn't encounter so many mistakes in the German exercises (but I still reported quite a few), since I went through them rather quickly. But in the French course there are still a lot of them. I wouldn't recommend to use it to anyone who doesn't already have some solid knowledge of French. As for Spanish: I don't know exactly, because I'm not fluent enough to spot all mistakes that are possibly there.