Indeed i put black clever twice but i never buy it twice.
I can buy 2 Bloodthirster or i take an item for tank a little more :D

There's no point in getting both Last Whisper and Black Cleaver. In League of Legends, the median armor is approximately 75. With five Black Cleaver stacks, you bring that down to 15, and your runes bring it down to -10. Last Whisper does ABSOLUTELY NOTHING at that point. Sure, it helps against tanks, but just a single Black Cleaver or a single Last Whisper is far, far more efficient at doing the job, given the amount of gold you spend.

By the way, getting two Black Cleavers does NOT let you stack the passive up to 10 times. It only means you inflict 2 stacks of the debuff with every attack, so you get to 5 stacks with 3 attacks instead of 5. Pretty bad idea to get two of them - if you're looking for attack damage, stick with a Bloodthirster.