The locale set in the notification affects only number and date formatting, notification content is not translated.
So it seems I have to translate all the text by myself, what is Name, Description, Subject and Content.
Hello! Our consultant has installed the ESMC in German language, so that all mail notifications are in German language. As we are an international company, I would like to change them into English, but that seems to be impossible without reinstalling the ESMC. Can anybody help?