"You swim still faster" is not grammatically correct in English. If you are trying to express the idea of someone being able to swim faster, regardless of X circumstance, you'd write "You still swim faster." This is one of those questions that trips up native English speakers, because now we have to remember which answers were not grammatically correct and how they were phrased, instead of focusing on word structure in Czech and taking note of patterns there.
Sorry, I do not understand what you are trying to convey. Do you suggest any change or something? Where do you see any still? I see even above.
Or do you just complain about the hints which show multiple translations of a word? That is quite common, dictionaries do the same. Not all the translations from a dictionary are applicable in any given sentence.
I would disagree that "You swim still faster" is incorrect. It means the same thing as "You swim even faster." As in, say, "I swim fast, but you swim still faster!" Though "even" is probably used more often.
On the other hand, the word order "You still swim faster" is more along the times of "Once up a time, you swam faster than I did and, in fact, you still do... even ten years later!"
But I guess it doesn't matter much if the system doesn't want "still" in the sentence! :-)
UPDATE --- I just got his one again, used "You swim STILL faster," and my translation was accepted... hooray!