This was really just a bedtime pen and paper problem that took about twenty minutes to solve.
We were at first a bit surprised that the cipher was so different in the Swedish version of The Code Book. Then we realized that Stage 1 was in the same language as the rest of the book. This meant that the plaintext was in Swedish in the Swedish version. It was later confirmed on the mailing lists that in most editions of the book, the first stage had been translated to the language in which the book what printed in
However, it turned out to be the same plaintext as the English one but in Swedish translation. This actually was a little bit intriguing since it clearly meant that someone else than the author had knowledge of the ciphers. Would this be true for other stages as well?