In Japan we call selective mutism Sentakusei Kanmoku or Bamen Kanmoku. They're very difficult words to spell and read.
I guess even many native Japanese can't spell or read these words. That's one reason why few Japanese know selective mutism. These words appear on a Japanese book Can you read these Kanji? -Check your degree of Japanese-.
It's difficult to change the words, because these words take root among child psychiatrist, educational psychologist, educator, etc.
On the other hand, people in English-speaking countries call selective mutism "SM." How simple!
Index of SM in Japan
