En gros, et en anglais
1) Increases the chance for successful ambush providing +1% bonus to Reputation for every point of luck. This effect does NOT increase your hp.
2) Increases the chance for successful quest. Every 5 lucks adds +3/+2/+1 % respectively.
3) Increases the chance to loot a preffixed/suffixed item.
4) Increases the chance to find more items in a quest. For example in 5th zone you can find either one or no items so the more luck, the more chance to find at least one.
5) Increases the chance to find a better quality item on Necropolis type realms.
6) The difference in luck between player during combat increases the critical strike chance::
Chance for critical hit = (Luck A - Luck B)/5 * 1%
(where A and B are player) Do not forget that critical strike chance is capped at 85%
7) The difference in luck during combat modifies minimum and maximum chance to hit. The player with more luck gains bonus to chance to hit while the player with less luck recives penalty equal to the bonus of the first player.