In my experience, that happens when people consciously manage the way they use their language, or have the trained instinct to do so unconsciously. At a certain scale choice of language doesn't really influence this all that much (as long as the language isn't Perl I guess, I've never seen that done cleanly.)

I've worked on really neat big Scala codebases and really terrible big Go codebases – a determined developer can make a mess regardless of language, and for some cases it's actually easier to end up in that place with Go than with a more expressive language with a more comprehensive stdlib. Go isn't well-equipped for a number of things, and if you have to do those a lot, generated code and workarounds like the pseudo-sets people build from maps really become liabilities.

From what I've seen as far as complex codebases are concerned, I'd say Go can be very readable for small-ish programs that lend themselves well to Go's opinionated standard library and way of doing things, but I'd definitely want to use something more expressive at scale or for anything that doesn't fit into Go's limitations well.

I couldn't disagree more. Everything I've read in Java was a huge messy pile of spaghetti code. C++ and C can definitely become unreadable very quickly. Rust, on the other hand, I find harder to mess, although there are still lots of ways to do it. And then there's Golang, I've read so much Golang code that I'm surprised when I run into something that isn't readable. Happened to me once, obviously the code had been written by Java developers (factories lol)