"We are not popular."
Translation:Nós não somos populares.
Why is "popular" also ok? I thought it would have to be plural in this case.
I think it's a mistake. I've tried to look it up on the internet, but most hits were false-positives. Only a few were actual Portuguese pages with ‘popular’ used as if it were a plural and even native speakers mess up every now and then.
I was going a bit fast when doing the exercises and simply put, "Nós não somos popular" and it was accepted... which surprised me because nano-seconds after hitting enter I realized it should be plural "populares" instead.
So, is it an error (on DL's part), or can "popular" be used in this case (and if so then with other plurals too)?
No, it is an error on DL's part. Your mind was faster than Duo =)
I don't think being popular should some under ser as it is something that can change so it should be under estar. Shouldn't it be 'Nao estamos populares'. Please forgive the missing accent.
Being popular or not is considered to be sufficiently permanent that ‘ser’ is used, same as with jobs for example. It's considered to be part of your essence rather than your state and that's the real criterion for when to use ‘ser’ and when to use ‘estar’. Being popular or not is part of who you are as a person, it isn't like being in Portugal for example.
I've found some uses of ‘estamos populares’ but those all seemed to indicate a tenuous, possibly fluctuating popularity, like a politician's for example. It certainly shouldn't be accepted as a translation for this sentence since it carries additional meaning and connotations not present in ‘We aren't popular.’
By the way, if you have trouble entering accents, switch your keyboard layout to US International. Then you can enter accents by first typing the accent and then the letter, for example first ~ and then a for ã.
Not that this is authoritative, but in Spanish we would use "somos popular" also, so it may be the same in Brazilian Portuguese. It sounds natural to my ears as a Spanish speaker. That's only right about 75% of the time though :)