Could you please add Common Lisp as a language? The SBCL implementation is the most popular Common Lisp, and has been for some time, and it is very performant! It is also mostly maintained by a Russian, Stas Boukarev. Common Lisp has been around for a very long time and its ANSI Standard has been the same for quite a number of years, so there likely would not need to be many updates after it is added once.
Adding the SBCL implementation as a supported language would be greatly appreciated by me and the Common Lisp community to be able to solve the amazing problems on this website with this very performant meta programming language. While attempting to get SBCL added, this repo could be used for reference -- I am also hoping to get it added to Kattis. I hope you will consider it.
**** UPDATE: Kattis now supports Common Lisp https://icpc.kattis.com/help/lisp