< Snigfarp>
My initial translation:
The castle can PREVENT, just like a third piece, that when a soldier stands on 2 (f.i. e4) and an enemy is on 3 (f.i.e3), it (the soldier) could be killed.

I'm sorry, maybe I understand you wrong, but the literal meaning is just the opposite of "a piece can be captured by a single enemy against a central square, as some reconstructions have it."

Do you mean you find the translation of "intercludere...ut" with "prevent...that" incorrect?
"intercludere" has several meanings (http://www.dictionary-translator.com/english/Lat
in-English/i/intercludere%20--%20block%20up.sh
tml)
and I think a translation with "block" (the castle blocks (prevents) the killing of a soldier on e4 when an enemy is on e3) is quite literal. Indeed, I choose a translation that makes sence to me. A translation like: The castle can seperate (some-one), [...], so that if a soldier stands [...etc...] it would be killed", doesn't make sense to me in the game.

My later addition had the following rationale:
One could assume from my translation of this rule that a soldier next to the castle is absolutely safe. I THINK though, and tried to argue, that this is implausible. It just handles the situation of a soldier between castle and an enemy, and that the castle "protects its neck". It doesn't say anything about the sides (so the other rules apply).
I don't see my addition as a correction, however. It is meant as a clarification of how brainking rules and lin. nr. 14 are compatible.

I hope I didn't totally miss your point? Please tell me when I'm flooding the forum :)
I hope this discussion helps you with the book you are planning to write. It would be great when Tablut gets more attention!