When does the Language User Preference get used?

If the user set the language in their user preference to Spanish language, when does it get utilized?  Is it when they login to the system?

The user preference is used when you login through SSO (Single Sign On), so if you login directly through DATABASICS Login page then you would need to select the language and if you do not select it the default will be English. Once you select the language on login, the browser will set the login as that language going forward.    

If you login through SSO then the system will check your language user preference on login and set the language for the site.