While according to the Monaco Constitution of 1962 French is the official language of the Principality of Monaco, there is a dedicated Monaco language called Monegascu (to be pronounced Moo-nay-gas-coo) that is still spoken by about 15% of the population.
Monegascu is a dialect that takes inspiration from both French and Italian languages and dialectes. Monegascu came about in the Middle Ages when Italians from Genoa came to Monaco to make it a stronghold ; which attracted many people from Nice, Ventimiglia, Torino and the surroundings. Everyone spoke their own dialectes which therefore ended up enriching the unified language spoken in Monaco.
After World War II and until the 70s, Monegacu was seldomly spoken and almost disappeared. Nevertheless the dialect kept on being spoken by some local families and on May 15, 1982 HSH Prince Rainier III created the Academy for Languages and Dialectes of Monaco. Studying Monegascu then became mandatory at school which has allowed the language to stay alive.
You may have also noticed that street signs are written in both French and Monegascu, which helps keeping the identity of the Principality of Monaco and its origins strong.
The Monegascu alphabet has 23 letters only as the letters K, W and X are not used. Although similar to French, letters are not always pronounced the same way and accents are stronger in Monegascu.
Without forgetting of course what you probably have already heard, especially if you have assisted to a soccer game, Daghe Munegu: Go Monaco.
Welcome to Monaco!