You can add support for any GraalVM languages. See jsc/js-runtime for a reference implementation.

Task	Reference
Add the GraalVM libraries to your build.gradle	build.gradle.kts
Implement LangDef	JsLangDef.java
You will also need to create a LangSpecificModule through which module operations/info can be accessed	JsModule.java
Register your language to JSCore on mod initalisation	JsLangInit.java
Set up the mod to depend on JSCore	fabric.mod.json and gradle.properties

Note: in js-runtime, I've set it up to require JSCore and js-runtime to have the same minor version. This is because the graal.* library must be the same in the two mods. The graal.* library version on JSCore will not change within the same mior version.