I've built production software being shipped to pharmaceutical companies and used in FDA submissions using Julia (pumas.ai) because it is quite mature in the field of modeling and simulation in comparison to other languages. The stability of the language along with the ability to easily get fast code is the main reason, and it's the reason why if you go to something like the American Conference on Pharmacology (ACoP) you'll hear lots of mentions of Julia.
I've also built several production systems and it has nothing but nightmare. Stack traces are meaningless and there were so many issues with things like ISO Time Zones, HTTP requests (why isn't there a solid http request library? its a mess), Docker problems with compilation, start times were atrocious and still are I think, package management is insane, setting up an internal julia repository is a total nightmare - just go on SO and search for it.
