if the number crunching requirements are moderate (e.g. can be efficiently done in NumPy OR can be done <1min runtime in cPython interpreter and there are no real time requirements) it certainly is very questionable to go with Fortran. If the above isn't true, e.g. for some heavy physics calculations, Fortran is still a fine choice if you get the right people to maintain it. I'd choose it over C/C++ but would first have another look at Julia (esp. regarding its tooling maturity).