I Believe in Santa Claus

J'ai rencontré le Père Noël is a 1984 French musical science fiction fantasy film directed by Christian Gion and co-written with Didier Kaminka. It stars Karen Cheryl, who was a popular singer at that time in France, as both the schoolteacher and as the Fairy. She acts and sings musical numbers in the film, an opportunity for Cheryl to repeatedly sing simple melodies, in line with the plot.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.