It's not purely a language thing per se, i.e. there are ways the language could change minimally but error messages could have a huge leap in improvement. However, certain idioms in the standard library might need to change, and certainly changing the language at the same time can improve the error messages even more.

I have only a little experience with Guix (replacing Nix with Scheme), so I'm not very confident in this, but the shallow impression I have is that Guix's error messages are not much better.