FcLangSetHash - return a hash value for a langset
#include <fontconfig/fontconfig.h>
FcChar32 FcLangSetHash (const FcLangSet *ls);
This function returns a value which depends solely on the languages supported by
  ls. Any language which equals ls will have the same result from
  FcLangSetHash. However, two langsets with the same hash value may not
  be equal.