A building with a French inscription
French was a major language of Earth, primarily spoken in France, but also popular in other regions, such as New Orleans and Quebec.
In 2152, Hoshi Sato answered an offer by Ravis to visit a steam pool on Risa with avec plaisir (with pleasure). (ENT: "Two Days and Two Nights")
Upon hearing Lieutenant DeSalles French name in 2267, Trelane asked him in French if he were a real French and exclaimed "Vive la gloire. Vive Napoleon". (TOS: "The Squire of Gothos")
In 2268, Cyrano Jones said "Au revoir" when departing a meeting on Deep Space Station K-7. James Kirk later used the phrase on his own departure. (TOS: "The Trouble with Tribbles")
French was also spoken on 892-IV. One Roman-influenced building on the planet's surface had the words "Honneur et Patrie" ("Honor and Fatherland") inscribed on the facade. (TOS: "Bread and Circuses")
James Kirk used an Earth expression, C'est la vie, while speaking with Kruge to describe the unfortunate destruction of the USS Enterprise and Kruge's boarding party. (Star Trek III: The Search for Spock)
By the 24th century, French was considered an archaic language (TNG: "Code of Honor") but was still spoken to some extent. (TNG: "Family") As a native of France, Jean-Luc Picard was fluent in the language, including folk songs and curses. (TNG: "Disaster", "Elementary, Dear Data")
In 2364, the holodeck character Minuet engaged Captain Picard in a conversation in French. In their brief dialogue, both Picard and Minuet remark, "Nous sommes tous Parisiennes," meaning "Everyone's a Parisian [in spirit]". (TNG: "11001001")
The holographic gangster Cyrus Redblock from the Dixon Hill series of holoprograms said "Au revoir" and "Bonne chance, mon ami" before he left the holodeck and dissolved in a corridor of the USS Enterprise-D. (TNG: "The Big Goodbye")
After time travelling from 2368 to 1893 San Francisco, Data identified himself as a Frenchman, and spoke French with a native speaker of the language, Frederick La Rouque. (TNG: "Time's Arrow")
Odo learned French in late 2374 from Vic Fontaine. The Changeling believed it to be "the language of love". (DS9: "His Way")
The Gigolo in the holographic program Paris 3 (Chez Sandrine) spoke French, mentioning terms such as "Mon cherie" and "Reculez-vous". (VOY: "The Cloud")