Dedicated config languages are the best usually. Jsonnet/Cue/friends.
Failing that if you actually need/want a procedural/non-pure language then I think Kotlin or Ruby take the cake. Both have extremely strong support for DSLs which IMO is key to reaching a modicum of usability.
Starlark is nice as well, it’s syntactically based on Python, and behaves a lot like regular procedural languages, but it’s meant to provide a pure and safe environment for configuration and be embeddable.
Big +1. We switched to Starlark for our DSL last year and have been very pleased. Users who've never used Starlark before come in with some 'what, another language?' trepidation, and end up pleasantly surprised.
Since using Bazel a bit I have grown an appreciation for Starlark also. The big thing is that list and dict comprehensions are a really nice fit for these types of tasks.
Failing that if you actually need/want a procedural/non-pure language then I think Kotlin or Ruby take the cake. Both have extremely strong support for DSLs which IMO is key to reaching a modicum of usability.