One of the most famous introductory CS courses in the world, MIT's "Structure and Interpretation of Computer Programs", was for decades taught using a programming language called Scheme, a dialect of Lisp that's wildly different from any mainstream language and is used for basically nothing other than this course. This was partly intentional, since it does a great job of shocking teenage hacker wannabes out of their "I already know language X so I'm hot shit" complacency.