Although Harry and his friends do not seem to learn any foreign languages at Hogwarts, they often use Latin. Almost all the curses, spells and charms derive from Latin words. The charm ‘Lumos’ for example, which causes a light to appear at the end of the wand, means ‘light’ in Latin; ‘Nox’, the command given to extinguish this light, means ‘darkness’.
Even two of the three forbidden curses are in Latin: Crucio, a curse which causes pain, in Latin means ‘torture’; Imperio, which makes the victim do whatever the curser wants, in Latin means ‘command’.
This ‘dead’ language is used in many ways throughout the seven Harry Potter books. Hogwarts’ motto “Draco Dormiens Nunquam Titillandus” is Latin for Never Tickle A Sleeping Dragon.
Latin was once a very widely spoken and important language. When the Romans conquered almost all Europe, Latin was a common language across the Empire. Scholars used to study it at school, thus almost all books were written in this language. It was also the main language of Christianity.
Modern ‘romance’ languages like Spanish, Italian and French, are descendants of Latin, whilst other European languages have acquired many words from it. More than 30% of English words have Latin roots.