The French language was spoken primarily in France, but also other regions across the world and taught in many high schools in the United States.
Westbridge High School offered French class. Sabrina Spellman and Harvey Kinkle were in the same French class in the Spring semester of their junior year. Sabrina once dreamdropped on Harvey having a nightmare about a French test in the class. ("Sabrina, the Sandman")
While her life was being tampered with by an other-realm TV producer, Sabrina encountered a Dinosaur that was terrorizing Westbridge High School that spoke French. To better converse with it, she magically made herself fluent in French. ("Sabrina's Real World")
When Hilda was turned to stone over losing her true love, Zelda conjured French sculptor Auguste Rodin to reconstruct her. When he commented he was finished in French, Sabrina was quick to translate, noting "4 years of French." ("I Fall to Pieces")