I don't think the "translation system" alters anything. I believe it has a set of phrases it probably checks against which is why you can report a "wrong" answer. If enough people are submitting a certain answer, they probably add it to the list to check against.
While I don't think your answer is wrong, as a standalone sentence it feels weird.
If I were pointing at something and talking about it, I would always choose a structure such as "Pillows like that are comfortable." over "Such pillows are comfortable."
I would use your sentence if it were preceded by a another statement regarding the pillows that would allow such a follow up.
- "My favorite pillows are goose-down. Such pillows are comfortable."
TL;DR While not grammatically incorrect, I wouldn't hold out hope for such a sentence structure to be the default translation.
Such statements are subjective and regional.
As a native speaker myself, I've heard it a few times.
"Such determination!" instead of "This/that determination!"
"Don't say such things!" instead of "Don't say those kinds of things!"
Personally, I like it more just because of how concise it makes things.
Accepted answers have phrases like this kind of where it's this because kind is singular, and pillows like this or pillows like these because both those work in English. These pillows are comfortable doesn't work though because that doesn't translate the sentence – that would refer to some specific pillows and it would be De här kuddarna är bekväma, but that's not what the Swedish sentence says.