I started by checking how you can write HTML using Kotlin DSL. Here is the source code https://github.com/Kotlin/kotlinx.html

Now, I have to generate different languages once the DSL is finalized. To achieve this I use Flask framework architecture. There we have routes with HTML templates. Here each generator has its own templates.

Not familiar with GPs use case but TypeScript has a glorious compiler API that could handle the heavy lifting here.