The list of official, available bud extensions:
The mdx extension is similar to what you are looking for.
Note that bud (currently) uses webpack under the hood,
so you can write a bud extension that uses a webpack plugin or loader to render a language to HTML, e.g. GitHub - zimmo-be/twig-loader: Webpack loader for compiling Twig.js templates.
Related discussion: How do I configure bud properly? - #6 by ben