Dan Fandrich has compiled an impressive list of languages available for classic (non-PC, non-CP/M) Commodore computers. There’s more than you may think, and, as you are likely to ask right now, yes, there is MUMPS (spefically EM for the SuperPET by Eclectic Systems, 1982). Where available, there are contact links and links to archives or repositories.
A very nice list! (More than a couple of dozen languages, I think, but with very many implementations of some of them.)