A couple days ago i was playing the tcg and a kid used bellsprout temple well
i know it giveseveryone a colorless resistance and when he used his chansey's
double edge he did fifty to and only fifty to him. Is that correct or should
he still have done 80 to himself

Well, my efforts to find a reliable translation failed, but if you are correct in your translation, then yes - Chansey, having a resistance to himself, would only do 50 damage to himself.

Scott