Easy level uses all 44 (11 each)location cards. Normal reduces it by 4 making sets harder and reducing the number of turns. Hard reduces the location cards again by 4 (now 9each). Again increasing the difficulty.
All of the above is detailed at the bottom of page 4 of the English rulebook under point 5, "Set the game's difficulty". I can't speak for any of the other language translations, but I assume it's in the same place.