Here's some food for thought from the Online Etymology Dictionary:
Meaning "to delight" in English is from late 14c. Inverted use for "to be pleased" is from c.1500, first in Scottish, and paralleling the evolution of synonymous like (v.). Intransitive sense (e.g. do as you please) first recorded c.1500; imperative use (e.g. please do this), first recorded 1620s, was probably a shortening of if it please (you) (late 14c.). Related:Pleased; pleasing; pleasingly.
Verbs for "please" supply the stereotype polite word (e.g. "Please come in," short for may it please you to ...) in many languages (French, Italian), "But more widespread is the use of the first singular of a verb for 'ask, request' " [Buck, who cites German bitte, Polish proszę, etc.]. Spanish favor is short for hace el favor "do the favor." Danish has in this sensevær saa god, literally "be so good."