Depends on what you mean by "100-year language". If it's in the pg sense (i.e. a language that's on the main branch of the evolutionary path of programming languages) I think the answer is clearly the ML family.

If you mean "what language is most likely to be around in 2100 AD", realistically we'll have C for as long as we'll have computers.

Lisp has a 20 (25?) year head start; it's not more dead than usual.

I was thinking probably Cobol will be first since it has at least 63 years already but apparently LISP is technically a year older. Fortran is a year older but I'm not sure it will last as long as Cobol/Lisp (it's losing out to python for simplicity and is likely to bleed a lot to c/c++/rust for science libraries/things that require faster glue code)

SQL!