I'm not sure I buy the notion of, "Solves the two language problem." There is always going to be some library or environment consideration that makes a unified language for everything impractical (unless your entire business runs on an AS400).
https://docs.julialang.org/en/stable/manual/calling-c-and-fo...
Even there you got support for C, C++, Java amung others as well as the whole IBM family (RPG/ILE, CL, REXX, ...) With somewhat decent bindings in RPG.