I would say those depend nowadays, I know of banks that have their IT infrastructure updated. But then again those are also new banks, not the old ones

Yeh, I know someone, is a friends Father, who is past retirement and getting paid a very healthy retainer to maintain a well known inter banking transaction system. He cut his teeth during the 60s / 70s. I would guess COBOL and pretty sure Fortran was mentioned also, was a while back we last spoke.