On the platform consumer side (app infra description) - well schema'd yaml, potentially orchestrated by helm ("templates to hellish extremes") or kustomize ("no templates, this is the hill we will die on").
On the platform integration/hook side (app code doing specialised platform-specific integration stuff, extensions to k8s itself), golang is the lingua franca but bindings for many languages are around and good.
On the platform integration/hook side (app code doing specialised platform-specific integration stuff, extensions to k8s itself), golang is the lingua franca but bindings for many languages are around and good.