I don't think it was mistranslated. Completetion of the books puts the weapon at the point where it matches its ilevel. There's 0 reason not to complete all the books (especially since it's not going to be the end of the quest). At some point, probably 2.3 there'll be another stage and I imagine it'll be something along the lines of being able to pick a customized 5th stat. The Zodiac line is going to span multiple patches.