The language is CUE, which I think will see mass adoption in config / DevOps in the coming years. So regardless what you think of the language today, it is likely to become important and part of your like in the not too distant future.
That's great context. That should be added to that doc link right at the top, it would have me feel much more safe about investing the time to learn it!
CUE has good pedigree, the creator Marcel wrote the prototype for Borg (k8s), worked on both Google config languages, and worked on the Go team. CUE is how he thinks those Google config languages should have been designed.
https://cuelang.org | https://cuetorials.com
Dagger builds on top of CUE and the (DAG) flow engine therein