I'm talking about real software systems with, at a very minimum, tens of thousands of lines of code. More realistically, we're talking systems with hundreds of thousands, if not several million, lines of code.
C++ can scale up to codebases that large. Java and C# can handle it, as well. Even Python and Ruby can, if care is taken. JavaScript cannot. You'll be hitting numerous maintenance barriers far before then, when you're still well under 10,000 lines of code.