The display language of system notification emails sent from Teachme Biz (information@teachme.jp) can be changed on a group basis.
Please refer to the following for detailed setup instructions.
Change language for email notifications (Web Browser)
https://teachme.jp/8/manuals/14110566
[CAUTION]
・Only group administrators and group sub-administrators can change settings.
・Settings cannot be changed on a per-user basis.
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Related: What should I do if I'm not receiving emails from Teachme Biz?
https://help.teachme.jp/hc/en-us/articles/900005508026