[jharsman]

Provided you still have source code and development tools available, the problem in cases like this usually isn't the language. Even APL is pretty easy to pick up if you have a book or someone to teach you.

The bigger issue is that the application you need to fix is mission critical, undocumented and contains massive amounts of spaghetti code. There usually aren't any tests, source control might not be used and it's far from certain there are automated builds or deploy scripts.

In some cases you might not even have source or the tools to use it, and then you have much bigger problems. But the language usually isn't the main problem.