Members can receive messaging in his/her preferred language. To update your language preference in personal settings, please visit this article - Update Language Preference. Updating the preferred language in Personal Settings will override the correspondence language pulled from the SIS.

Another helpful article: What Languages are Supported

If you're an Administrator looking to change the language preference for another member, this information is pulled from the SIS, although some Admins have the ability to update preferred languages within 
Dashboard - Members.