Is the C language still used in management systems as it was used?
There isnt anything significantly better for writing programs in that space, and theres a lot of code already written that would take a long time to replace. If you were starting from scratch, you might well use a different language, as there are options, and the number of platforms youd need to support is much smaller, so Cs portability is less of an issue/advantage than it once was. I dont think you could use Go very well, and C++ has its own, um, legacy. Rust would be plausible. I liked D, but it seems to have faded. Dont know about Nim. It would possibly be illustrative for some Professor somewhere to slowly build up a Rust SQL database in modern form over the course of a two or three-book series.