Playing a sound when you say "thanks" in a message, anime girl saying : Arigato.
To get the sound, create a folder named : CustomSounds in WorldofWarcraft folder, you should have something like that : World of Warcraft\_retail_\CustomSounds.
Download the audio file :
https://drive.google.com/file/d/1fXTOLlXwHDfv98_H0v_TZeGKQiUSFf5y/view?usp=sharing
Then put it in your CustomSounds folder, exit the game, close the launcher and relauch, then enjoy :)