Translation (know russian very good, but can have problems with english
):
Intellect for hero.
For offensive spells every point of intellect increases your damage by 10% and for every 7 points of intelect summary damage is increased by additional 10%. For "duration" spells every 15 points of intellect increases spell duration by 1 round. For spells which have additional effects (like burning, shock, freezing and poisoning) with certain probability to be applied every point of intellect increases effect applying probability by 1%.
All except last sentence was in intellect description as i remember.
And "summary damage" means that 10 additional percent are calculated from damage which have applied 10% bonus for each intllect point:
dam=basedam*(1+0.1*int)
*(1+0.1*floor(int/7))