It is absolutely not correct in practice. While it's not technically wrong to use rätt like that, it is not used by natives and should not be taught to learners.
Quoting the Swedish language council:
In theory, it should be possible to inflect rädd like that, but that is usually never done. Another word is used, or the the whole phrase is rewritten, e.g. as ett skrämt barn. [...] From a language cultivation perspective, there's nothing remarkable about forms like rätt and morbitt. They're just never used by anyone.
I am a native, too, and I trust the Swedish language council's advice. You do realise that Wiktionary quotes the same page as I did? From Wiktionary: "The language council comments on the neuter form rätt and ascertains that it is not wrong, but that it just isn't used." Again, it should not be taught and it is not in common use.
Edit: The above comment has been changed since I replied to it. It said something else originally.
I read somewhere that there is a quite serious mistranscription of the famous first scene of Det Sjunde Inseglet (The seventh seal). It goes like this in the BlueRay:
RIDDAREN: Vem är du? (Who are you?) DÖDEN: Jag är Döden. (I am Death.) RIDDAREN: Kommer du för att hämta mig? (Have you come for me?) DÖDEN: Jag har redan länge gått vid din sida. (I have been walking by your side for a long time.) RIDDAREN: Det vet jag. (That I know.) DÖDEN: Är du beredd? (Are you prepared?) RIDDAREN: Min kropp är rädd, inte jag själv. (My body is frightened, but I am not.)
But some people complain that what the Knight really says is: "Min kropp beredd, inte jag själv." (My body is prepared, but I am not) Which is the opposite of what the English speaking audience is getting.
Could anybody please tell me if this is true? He speaks so fast it is quite difficult to say. (start in 0:50) https://www.youtube.com/watch?v=N7oj9JkcRGc
Arnauti, devalanteriel, I think you both are right. I found this: http://www.ingmarbergman.se/verk/det-sjunde-inseglet/media/
The controversial sentence is in the following page, but touching it a bit with Photoshop you can read "Min kropp är rädd":
And also this:
I was surprised too! This is like a doctor's handwriting not an artist's, isn't it? It is quite chaotic. I don't know what it means. What kind of personality do you think he had, according to this handwriting, Arnauti?
By the way, are the two dots (umlaut) usually written that way, as a little dash? Maybe when you are writing quiclky in Swedish you need to simplify dots and rings. :)
@myriam365 Whether or not you use dashes or dots for the umlauts mostly just depends on your personal handwriting. When I write in cursive, which is my personal handwriting, I use dashes, but when I write in non-cursive for example for my printed name I use dots. Å always has a circle on top though.
Wow, I think I just found a photo of the original script: http://www.ingmarbergman.se/verk/riddaren-och-doden And it says "beredd"!!
True, nobody agrees. :) These say it is "beredd": https://sv.m.wikiquote.org/wiki/Det_sjunde_inseglet http://gits.blcklst.com/comment/wp_post_13325.html
Myriam and Arnauti, I don't find his handwriting surprising. He was a 4w5 in the enneagram according to Don Richard Riso and I am a 5w4 which is the same but with different emphasis. I don't think doctors write like that at all. He definitely has an artistic-intellectual temperament from his handwriting.