This is unnatural in English. Some people probably would say this, but I would say, "My room is free of dust."
I agree. This sentence is not technically wrong in English, but it sounds very stilted and unnatural. Rebecca's translation works better, as well as "clean and dust-free" or "clean and without dust."
In addition to the above comments, we should note that there appear to be a number of Hebrew speakers who are using this DL course to improve their English. So, while perhaps not the highest priority, we should try to have the English parts be as well written as possible.
I am quite happy to use the literal translation. After all, the point here is to learn Hebrew, not English. If you are trying to improve your English, however, it is good to know the other options.
I don't think anyone is suggesting the literal translation shouldn't be allowed, but that the idiomatic (and more natural/better) translation should be accepted.
The person trying to learn Hebrew should not have to use unnatural/poorly phrased translations to be marked correct. If a more natural translation exists that clearly expresses the same meaning, it should be accepted.
I suggest a compromise to the comments already given: Duo could add "my room is free from dust" as another correct solution, without taking away the literal one and/or the other way around...
Agree. Or 'free of dust'. ('free from dust' doesn't sound quite right to me.) Anyway, colloquial translations should be accepted. English speakers just wouldn't say 'clean of dust'.
An English speaker wouldn't say that. 'Dust free' or 'free of dust' is what I'd say.
I agree with most of the comments here. Although this course is about Hebrew, not English, it's silly and counterproductive of DL to mark a perfectly correct English translation wrong, or to insist on an English translation that's incorrect or very stilted.