The big issue is the presence of cyclic dependencies between parts of code. If a piece of code is identified by its content, and its identifier is the Merkle root of its parts, then you can't possibly have cycles because you can't compute the hash of a parent before computing the hash of its children (which in turn depend on the parent). You have to use DAGs or plain old trees and eliminate any cycles.

So to get it to work with other languages, you would need a way to convert their abstract syntax into a DAG compatible structure. It may be possible to do so, but I doubt there is a general approach which will work across multiple existing languages. It would require per-language hacking, if it is even possible without rewriting some parts of code.

Seems like languages like OCaml and F# might be slightly more suitable for this approach because they require compilation units to be ordered by their dependencies, and thus promote a convention of avoiding cyclic dependencies between types (although it is possible to make such dependency in the same compilation unit with `type A and B`). They also allow recursive functions, but these should be simple enough to represent with a non-cyclic syntax tree.

If you design a language from scratch, you can simplify things by requiring that no cycles exist in the language - at least at the syntax tree level. You might be able to design representations for recursion at a higher level which collapse to non-cyclic structures in the AST.