Is a story written in an archaic and high-strung tone readable?

I plan to write an Medieval swashbuckling-story. The Idea for the narrative is what's essentially the unholy union of Flowery Elizabethan English (or rather its Swedish equavilent) and Antiquated Linguistics . I would have liked to have written some English text in the style I planned to use to show you all what I mean, but unfortunately I'm apparently not that fluent in English yet... For all you Swedes out there: The Swedish Viking-novel Röde Orm Swedish version is the tone I want to emulate.

I'm well aware that only using words that dropped out of common usage well before the reader's were born & some people might not even know might be a bit problematic, but would anyone be discoruaged to read it by this kind of writing-style?

Sadly, a lot of people probably would be put off/discouraged. You'd have a niche target of people who enjoy reading old texts (as opposed to the modern-language translations) - and not all of them would read it because it's not a genuinely old manuscript.

Modern people - English speakers, anyway, and I'm guessing modern speakers of other languages would be similar, YMMV - prefer to read their own version of the language and understand it without having to work (like stopping to grab a dictionary of archaic words, which rather breaks immersion).

Even if the story is set in Neolithic times or ancient Mesopotamia, Translation Convention has them speaking in the default, current, language that the book is written in. It's what audiences expect, they want to be immersed and the easiest way to do that is by using language that is so simple to comprehend that it becomes transparent.

Books written in old flowery language were once the simple, transparent, understood by all (at least by all those who could read or knew someone who could read it to them) language - but that hasn't been the case for years as the languages have all moved on.

Shakespeare, Chaucer and such, as hard as they are for some to read these days, were written in the vernacular of the time, as our modern authors do.

That's not to say that your book has no merit or won't have any buyers at all, just that the buyers will be limited. The question you then have is: 'do I want to create a work of art that requires me constraining myself to a particular style (and doing it well) and getting accolade from the few people who can appreciate it or do I want to make a popular novel that sells well and earns me a room full o' cash?'

I understand you totally, and writing exactly the way they did back then is usually idiotic, and I'm aware of that. I have read 500 year old text and they do not make for easy reading.

What I meant was that I do not plan to write in a super-archaic style based on the Middle-ages, but rather the style of 150-200 years ago. (Espescially since Swedish had a spelling-reform 100+ years ago that changed spelling & endings slightly.) Writing from before that spelling-reform sounds somewhat a bit fashioned, but is still very understandable. An good compromize in other words. Throw in a few old words and it sounds "Medieval" enough.

I can get access to some books written in that style so I won't write random gibberish but something more or less correct.

I know nothing of Old vs New Swedish, so I'll take your judgement on that.

I have characters that hail from various eras - 1700s to present day - so I work to keep their speech correct for their eras, which entails using words that had different meanings or words that are now considered archaic and avoiding modern terms and meanings of words. Even then, I try to avoid words that would thoroughly confuse the readers and the body of the text is written in modern English.

Two things come to mind when talking about using archaic or obscure dialects of a language the reader speaks in a way that would work:

1. To make a point (or a joke) about how the language changed overtime or over the distances: in Good Omens, there are a couple of gags about a book written in 1600's or so and another scene that includes two British people, one American soldier and the word "faggots".
2. For verisimilitude's sake, when writing historical fiction. The Aubrey Maturin series was written by our contemporary and is so thoroughly and intricately researched and written, that some mistake it for being written in the times when the novels take place (The Wooden Ships and Iron Men era). Suffice to say that the target audience of such works expect some level of archaism in the used language.

I'm not Swedish, so I can't speak to how your native language readers may react, but I personally don't mind archaic tone or language in a book that's either historical or fantasy. In those instances, it feels more natural to me.