We have worked with LLVM a lot for own own compilers and DSPs.

LLVM Intermediate representation in practice is C++, AST is C++. LLVM do not support many languages,many languages support LLVM, which is different.

That is many people, or languages' designers, have made the necessary work to make their languages compatible with LLVM IR. If the language is similar to C++, this is a simple task, if it is very different, it is very hard.

LLVM does not support other languages, in fact, codebase changes a lot making maintenance painful.