Flowerese
From Nookipedia, the Animal Crossing wiki
Flowerese
Flowerese is the unheard language of flowers. Peppy villagers mention this language while talking to you sometimes, stating that they can hear the flowers when they water them and that it took such a long time to master Flowerese. You cannot activate the language Flowerese to be used on your phone in the atic, so it may just be a made up idea created my peppy villagers such as Bluebear.