Learn Danish = Literate in Norwegian/Swedish?
I'm starting to learn Danish. If I get really good (levels 22 and up) and be basically literate in Danish, how good will I be in Norwegian and Swedish? How long would it take to be literate in those two also?
I think it's a good idea to become literate in one so I can potentially have another 3 languages under my belt. Good idea?
Norwegian is mutually intelligible to a Danish speaker, Swedish a bit less so. Knowing 1 will however make the other 2 much easier to learn and pickup.
I wouldn't worry about levels, since Duo only gets you so far and you will finish the course quite a few levels before level 22.
Also an interesting read: https://www.babbel.com/en/magazine/the-scandinavian-languages-three-for-the-price-of-one
Level isn't really equal to literacy. That comes down to practice and vocabulary.
Norwegian has two written standards, Bokmål and Nynorsk. You'll have no problems with Bokmål as it's extremely similar to Danish. Nynorsk might take a little more concentration, but it's no great hurdle. Swedish is the least similar to Danish so it'll take some study to get used to it, but you shouldn't find it too hard when your Danish is advanced enough.
If you're just wanting to learn to read the other two, understtanding Norwegian will take very little time and a little mental effort. You could probably get used to the differences in vocabulary and spelling with Swedish in a matter of weeks.
Speaking is another matter altogether- if you can read, write, speak and understand Danish but only read Norwegian and Swedish, you don't really have three languages under your belt. Danish will be a lot less help than you think when learning to speak and listen to Swedish, but Norwegian, again, shouldn't be too much of a leap.