They use Go as well, I know someone who writes it for banks, but most of their infrastructure is written in COBOL. There are some sources [1], and some people have told me the same in person, not in exact numbers or percentages, but roughly the same.

Anyway point remains, electronic transactions with no internet or electricity is a solved problem, and banks don't want to solve it or they can't due to incompetency or maliciousness.

Currency transactions worth their weight in gold, it is of utmost importance for transactions to always be published to a central authority right away. If they don't have to be published, they should not exist at all. Imagine people buying stuff without anyone knowing right away! That should never, ever exist, for any reason.

[1] https://thenextweb.com/news/ancient-programming-language-cob...