"The old books have been shown."
Translation:De oude boeken zijn getoond.
It's a Netherlands/Belgium difference if I'm not mistaken. It's the same tense, but in the Netherlands the last word is usually left out. If you mean "what the rule used to be" by more grammatical correct, then you're right, but this is an example of how language changes. It means the same thing, but a different form is now in use next to the original longer form. Also in German it is said in full, and probably in Flemish as well. Is the form without the last word used in Belgium as well?
BTW "zijn geweest" is indeed correct, so if you come across sentences where it is not accepted, please use the report a problem button so we can add it as accepted translations.
With more grammatical correct i indeed meant that it was the rule before it got simplified. But now even the official language advisor from the Flemish government advices to use it in the way the Dutch do it. http://taaltelefoon.eu/veelgemaakte-fouten-vervoeging-van-werkwoorden So in that way i'm wrong :/
I have reported as much as i could today but it's up to you to decide what you do with it. I personally feel that the way you guys use it is a bit more in the present than the Flemish/German form.
I think in spoken language "geweest" and "geworden" are still used a lot but probably in written language it's declining if the Flemish government decides to promote the newer variety. (which for me has a more "present" feel to it)
The main reason why i brought it up was because i think it's easier to learn than the newer form since it corresponds better with other languages. :)
Thanks for the interesting reply. When talking about language I wouldn't say going against a government advice is wrong. Language is determined by the whole community of language users, so they determine the norm, the government doesn't. :)
Also thanks for reporting. The course is aimed at Dutch as spoken in the Netherlands, so we will use the Dutch Dutch form as the standard translation, but we also accept alternatives, so in situations like this where there is a correct alternative we try to add that as an accepted translation everywhere.