猫に小判 Give a Cat a Gold Coin
Cast Pearls to a Swine
houseki ni kyoumi no nai hito ni daiyamondo o agetemo, neko ni koban da.
For someone who has no interest in precious stones, even giving him a diamond would be casting pearls before swine.
宝石 houseki—precious stones, gems
興味のない人 kyoumi no nai hito—a person not interested in...
上げても agete mo—even if (you give him a diamond)