Is that true that if i pluck one white hair the two more will grow up?

No: Plucking a hair only affects one follicle, which can only grow one hair shaft. Plucking can cause ingrown hairs if you have curly hair, so in general this should be avoided.

No: That's an "old wives" tale meant to discourage rude behavior rather than espouse medical advice. There's no evidence that plucking a strand of white hair will create two strains. Though i don't recommend doing this in public, as the saying was meant to discourage this behavior.