I would love to see a language that considers tooling a first class problem. Most (all?) languages barely consider complex projects with 100s of dependencies and large multi-step builds. Java shouldn't have to wait for Maven and Gradle to come along, and Python shouldn't be shackled to piss-poor systems like pip.

This is something Rails gets very right. Bundler and Rake make Rails one of the nicest development environments there is.

But we can and should do better. Why is DLL-hell still a thing? Imports should specify versions, defaulting to a default if none is specified. Languages barely even consider versions today, they are almost always hacked on via magic text strings in filenames.

Why do tools like Dependabot and Renovate need to parse a million dependency formats to figure out versions? The language runtime or build system should produce that as a first class output.

Deployment and documentation are other places most languages ignore and delegate to a variety of crappy external tools.

Build Server Protocol is a good step in the right direction, but it barely scratches the surface. It would be great to see a language that prioritizes the parts of the developer experience that aren't writing code.