Then can you explain how it is a valid English translation of the phrase if it is not a correctly constructed English sentence?
It seems that to translate it to English you would have to include through implication the 'few' as part of the translation in order for it to make grammatical sense.
It’s a difficult balance between idiomaticity and literalness. In order for Duolingo to work, the translations have to be somewhat literal, since the concept is that you’re given the bricks and have to figure out the blueprint. If there are a lot of bricks that are implied it doesn’t work as well, since you’d have to know the language in order to know which words to add or leave out.
This balancing between trying to keep English translations as literal as possible from Swedish, in order for the brick concept to work, and still try to have the English translation as idiomatic as possible for English speakers is difficult, and it doesn’t always turn out perfectly.
Since we’re not here to teach the English language however, there are often many alternatives that are correct as translations from Swedish to English, so in this case you’re marked as correct both if you leave out or include the word ’few’ in this example.
Yes, that's correct.
Swedish has three words for "the": den for singular en-words, det for singular ett-words, and de for plurals.
Now, de additionally happens to be third-person plural pronoun - but that's a different word, just happens to share spelling and pronunciation. :)