Originally Posted by peripatetic
"Derecho" means Right in Spanish; "Droit" means Right in French; "Sinister" comes from the Latin, wherein "Sinistral" means Left-handed. I'd guess that you're looking for the Left pedal. Good luck, wish I could help you.
Campagnolo is Italian, so here's the Italian meaning:
S = Sinistra (Left)
D = Destra (Right)