Translation:The dog, which has six puppies, is trying to stand.
I think, it's not normal English. On the contrary, normal English refers animals as "it". From my experience, people tend to call their pets "he" or "she" because they don't want treat them as things. Sometimes people refer to, for instance, their guitar as "she" because they love it so much. But I don't think it makes this English normal.
Does a Finnish clause like the "jolla..." clause above only have "aside" meaning (e.g. "The dog (which by the way has six puppies) is trying to stand" or can it also have qualifier meaning (e.g. "The dog (the one that has six puppies) is trying to stand")? If both, then it seems like either "that" or "which" should be accepted in the English translation.
I used "that" instead of "which," and "that" should also be accepted but it was marked wrong. There's not enough context to show whether the clause is restrictive or nonrestrictive, so both "that" and "which" are acceptable. And you can't tell from the Finnish, because (apparently) there will always be commas setting the clause off, whether it is meant as restrictive or nonrestrictive. Reported.
I agree with those English speakers who suggest that we do not treat dogs as inanimate objects or unintelligent beings and that we would refer to them as 'he' or 'she' rather than 'it' and thus we would always say 'who' rather than 'which'. Perhaps Duolingo could learn to be more adaptable so that it could be correct rather than incorrect?