Earlier quoted context omitted.
> It's not a problem with "non-modern" languages, it's a problem with C and many of its successors. Not really. Any semi-decent modern language allows the creation of custom types which support the desired behavior and often some syntactic sugar (like operator overloading) to make their usage more natural. Take C++, for example, the archetypal "C successor": It's almost trivial to define a class which stores a fixed-…
It is also trivial to keep doing C mistakes with a C++ compiler, hence no matter how many ISO revisions it will still have, lack of safety due to C copy-paste compatibility will never be fixed.
Okay, no idea how that's relevant to "built-in decimal types" vs "library-defined decimal types", but if it makes you feel better, you can do the same in Rust or Python, two languages which are "modern" compared to COBOL, don't inherit C's flaws, and which enable defining custom number types/classes/whatever together with convenient operator overloading.