Translation:We are watching the girl playing the violin.
I would be against allowing "we watch how the girl plays the violin" not because it's wrong, but if it had accepted my answer I wouldn't have learned that it's how to express the complex object in general
I think if it was more literal then the importance of the construction might be lost
I can always add a reject message first. :)
The important thing is to not lose the meaning. For example, both "The ball is in the box" and "The ball is on the box" are correct English sentences but they aren't both adequate translations of «Мяч лежит в коробке». "Travel" and "make a journey" are similar but, probably, not in "Light makes a journey in a straight line unless affected by a gravitational field of a large mass".
It is a set structure. To express how you listen to or look at (hear, see) someone's actions as they do them, you use смотреть or слушать (видеть, слышать) and then use unstressed как to connect a clause. Usual Russian rules of sequence of tenses work (i.e. the verb will usually be in the present tense, because the verb of the clause is understood to be relative to the verb in the main clause)
If you need the literal interpretation of как badly, you use context to support your point or emphasise it in your speech (rewording will also help, naturally).. Think of this: there is a huge difference betwen closely watching someone, who is playing the violin (cops do it if they suspect somehing fishy's going on), and watching someone play violin (audience does this). Yet in English "We are watching the girl playing the violin" means both.
Admittedly, these sentences in the course are sort of artificial. In real life "X watched Y do something" would appear as a part of a larger story («Что ты делал?» — «(Я) просто слушал, как она поёт»). Unfortunately, long sentences are no fun on Duolingo, so we keep it simple when we can.
interesting... now I see. It seems that my question was more related to Portuguese than English, I guess...
so lets say I'm a violinist as well, but she have done a sound I have never heard before with the violin. I want to see how she does it so I could reproduce it. I'm watching specifically how she plays the violin. I mean, her technique. the chords, etc.
How would that be in Russian, if any different from the original?
"We are watching the girl play the violin" might be slightly better than "We are watching the girl playing the violin". The latter sentence is ambiguous: it could mean we are watching the girl who is playing the violin, as opposed to the girl who is playing the cello. "We are watching how the girl plays the violin" is a grammatical English sentence, but it means that we are either evaluating her technique or watching in order to learn to play ourselves, not simply "We are watching the girl (as she is) playing the violin".
It is quite peculiar to me this way of expressing what I would call an objective clause, and Duo has given several examples of that : the main clause (we're watching) becomes incidental, (followed by the comma) and the object of observation becomes the main clause: (We are watching someone doing something -> someone is doing something, we see ). Что or как are required in some circumstances. I'm looking for the next episode of the saga...