TooltipItemInfo is a very basic nonconfigurable addon that adds 2 lines to the tooltip of items.
One line with the itemlevel and one with the stacksize.
Check the screenshot for an ingame example.
Credits go to Tuller for SellFish. I took some of his tooltip hooking code.
if GetLocale() == 'ruRU' then
STACKSIZE_TEXT = "Количество в стопке"
ILEVEL_TEXT = "Уровень вещи"