No there isn't. Since you bought your Wii U in America it's only got English. Same in other countries. But it you're on your phone on Miiverse you can add Japanese keyboard like so (お元気ですか。元気です！素晴らしい!) and Korean if you wish (오늘 어때요? 잘 있어요! 훌륭해요!) and even Chinese (你今天感觉如何？我很好！真棒!)