I don't believe that's true, they have pkl in other languages, too, and I double checked it doesn't require the jre https://news.ycombinator.com/item?id=40146077 (tl;dr = https://github.com/apple/pkl-go/blob/v0.6.0/.circleci/config... which shows both pkl-go as well as how they, themselves, use a single-binary in a circleci setup)

I haven't tried to integrate pkl-go into something like glasskube so I am open to that part being painful because software gonna software, but I believe the general statement of pkl being Java-only is incorrect