So I assume you don't like many of the popular build tools at all - Make, bazel, etc all define a custom DSL effectively. At least Groovy or Kotlin are actual languages you can learn and use for other things, not something that has no alternative purpose so is completely wasted. And their syntax is very close to Java so you have a head start on learning it.

In general the concept of a "cross platform" build tool and "not having to learn another language" are at odds with each other, for anybody who isn't lucky enough to already work in the language the build tool is written in.