Code written in C89 can trivially link against code written in C18. This also mostly works in C++ as long as new features are not used at the interface level an

Code written in C89 can trivially link against code written in C18. This also mostly works in C++ as long as new features are not used at the interface level and you don't have an ABI migmatch (e.g. with stdlibc++ std::string, although that's possible to work around with proper configuration). Any language exporting a C FFI should work just fine.