Franel was a number theorist who gave introductory calculus lectures in French at the ETH. Maybe the ETH offered courses in different languages, because of its location in a multilingual country. Does anybody know? Anyway, for a little more information, see this excerpt from Jerry Alexanderson's The Random Walks of George Polya.
[Added later] At this site there is a list of all professors in the history of the ETH, between 1855 and 2005. Franel is not the only professor for "Mathematik in französischer Sprache" -- there were some before Franel, and others in more recent times were Beno Eckmann and Armand Borel. There were also professors of geometry, mechanics and statistics "in französischer Sprache". So, Franel was not at all special in this respect, which strengthens my suspicion that the ETH made a point of offering courses in French.