"no mainstream language..." COBOL is has not been a mainstream language for many decades now.

It's still quite mainstream in domains where they manipulate a lot of money : banking/insurance.

The core systems of many old institutions still relies heavily on COBOL.

I think I will add a footnote on COBOL. COBOL is huge in Brazil, lot of insurance/financial companies are still using mainframes.

There are billions of lines of COBOL in production. It's not going away any time soon.