If the language has "A real package system" why not allow for packages written in other languages? If a C build system can look at a .h and a .lib and figure o

If the language has "A real package system" why not allow for packages written in other languages? If a C build system can look at a .h and a .lib and figure out what symbols are exported and use them then I seen no reason why a compiler for xyz could not also do that. If you reused OSS projects like Clang it may not even be a monumental effort.