When a user signs into the portal, they are asked to choose their preferred language. It would be great if that choice were exposed for the admin. Being able to put people into a smart group based on their self-stated language preference would allow us to create Phishing and training campaigns with templates and notices in the user's preferred language.
This method is preferable to pulling data from Active Directory because it is user-selected. AD and any other form of getting this data (that I know of) relies on an administrator to set the user's preferred language.