I'm kind of confused by "už" here. I would expect the translation to be either "Have you ALREADY seen it" (which was accepted) or "Have you seen it YET" (which I didn't try).
But if the sentence can be translated as simply "Have you seen it," what does "už" add? And would just "Viděla jste to" be incorrect in an English-to-Czech translation?
I'm not sure that "Have you seen it?" is functionally the same as "have you seen it already?". In the first, the stress is on seen. in the second the stress is on already. Either way, the use of už in the Czech version should be translated as already in the english translation. my two cents.
If I may. Have you seen it. Technically means the same as Have you seen it yet or Have you already seen it I would say that the uz in the Czech sentence just indicates that one should use the Present Pefect to translate the sentence in English. The question is whether Duolingo accepts the translation with or without already or yet. My two cents.
There are a number of accepted alternatives that include "yet" or"already." I would agree with BenMedved that the meanings of "Have you seen it yet?" and "Have you already seen it?" are not identical in English. Both "have you seen" and "did you see" are accepted in this exercise, as discussed above.
Going back to the start of this debate, in English spoken in my part of the world, "Did you see it" and "Have you seen it" are pretty much synonymous. "Already" is not part of either question. Were we to be going in the other direction, I would expect the Czech translation of both probably to be the same and presumably not include "už" unless it has a special meaning in this context. So in my view, either it should be left out of the Czech statement we students have to translate, or it should be included in the optional words to put in the answer. That is my two pennies!