The phrase "The moon is beautiful, isn't it?" is a poetic expression of love originating from Japan. It's a subtle and romantic way of saying "I love you." The implication is that the beauty of the moon is a reflection of the speaker's feelings for the person they are addressing. Appropriate responses might include acknowledging the moon's beauty with agreement or offering a reciprocal sentiment, expressing a shared appreciation for the moment and the connection between the two individuals.