The term 'Hogwarts Motto Language' is referring to the LATIN language, which is a classical language that was widely spoken in the ancient Roman Empire. LATIN is still used today in many areas, including in mottos, legal documents, and religious ceremonies. The LATIN language is also used in the Hogwarts School of Witchcraft and Wizardry's motto, 'Draco Dormiens Nunquam Titillandus, ' which translates to 'Never Tickle a Sleeping Dragon.'