Should a user require notifications be sent in a specific language, you may set that language via the User Console. This can be done when you are adding a new user or later by selecting the user from the list and clicking on UPDATE from the bottom menu.
In the user information box, there is a dropdown for Default email language, as illustrated below. Select the language from the dropdown that you wish to use, then save the user profile. As noted in the information box, this is the language that will be used for email notifications to that user.