Translation:What juice do you want?
Yes, I’d translate the individual words like that too.
But translation works sentence by sentence. I would not naturally say “What juice do you want?”, especially if speaking to my grandmother. It would sound too casual, rude or ubrupt in some contexts.
“Which juice do you want?” is the sentence I’d use in English to convey the meaning of 你想要什么果汁？so it would be nice/helpful if it were also accepted.
Report any translations you make that you think are good ones. They add to the pool of accepted answers and make it better and easier for the future.
It can take a while for the volunteers who do it to review all the submissions but they do get to it eventually. I’ve seen a huge amount of progress in quality on duo over the time I’ve been using it.