Developer experience is just one facet of writing software. It means that it is pleasant to write code, but you can also focus on:

* Language features that make it so that you don't have to write code at all

* Tooling that makes it easier to find bugs in the code you do write

* Expressiveness and portability that allows the code to be used in more places

* Approachability, so that new people can pick up the language quickly

* "Batteries", so that people can rely on your high-quality libraries instead of having to manage their own

* Documentation and community, to handle the hardest parts of programming: people

* Performance, so that the code can use fewer resources

…among many other things.