#include <iostream>
#include <cstdlib>
#include <windows.h>

using namespace std;

int main()
{
    HINSTANCE dll_module = LoadLibrary("test.dll"); // загрузка модуля DLL

    if(dll_module == NULL) {
        std::cout << "\nLibrary NOT loaded!";
    } else {
        std::cout << "\nLibrary loaded.";
    }

    LPCSTR func_name = "GetLangId"; // название загружаемой функции
    FARPROC func_addr = GetProcAddress(dll_module, func_name);

    if (func_addr != 0) {
        std::cout << "\nfunc_addr = " << func_addr;
        // typedef int (__cdecl *int)(void);
        // func_addr();
    }

    FreeLibrary(dll_module);

    std::cout << "\n";
    std::system("pause");

    return 0;
}

#include <iostream>
#include <cstdlib>
#include <windows.h>

using namespace std;

int main()
{
    HINSTANCE dll_module = LoadLibrary("test.dll"); // загрузка модуля DLL

    if(dll_module == NULL) {
        std::cout << "\nLibrary NOT loaded!" << endl;
    } else {
        std::cout << "\nLibrary loaded." << endl;
    }

    FARPROC SetLangId = GetProcAddress(dll_module, "SetLangId");
    FARPROC GetLangId = GetProcAddress(dll_module, "GetLangId");
    int LangId;
    BOOL flg;

    if (GetLangId != 0) {
        LangId = GetLangId();
        std::cout << "LangId = " << LangId << endl;
    }

    if (SetLangId != 0) {
        std::cout << "SetLangId = " << SetLangId << endl;

        typedef BOOL (*SetLangId_funtype)(int);
        flg = ((SetLangId_funtype)SetLangId)(0);
        std::cout << "flg = " << flg << endl; // <<<<< ------- ЗДЕСЬ ВЫВОДИТ: flg = -1

        if (flg == TRUE) {
            if (GetLangId != 0) {
                LangId = GetLangId();
                std::cout << "LangId = " << LangId << endl;
            }
        }
    }

    FreeLibrary(dll_module);

    std::cout << "\n";

    return 0;
}

function SetLangId(id: Integer): BOOL; stdcall;

typedef BOOL (__stdcall* SetLangId_funtype)(int);

        typedef BOOL (__stdcall* SetLangId_funtype)(int);
        flg = ((SetLangId_funtype)SetLangId)(1);
        std::cout << "\nflg = " << flg; // <<<<< ------- ЗДЕСЬ ВЫВОДИТ: flg = -1

        if (flg == TRUE) {
            // --------------------------------------- <<< сюда не заходит
            if (GetLangId != 0) {
                LangId = GetLangId();
                std::cout << "\nLangId = " << LangId;
            }
        }

if (flg == TRUE) {

if (flg) {

function GetLastErrText: BSTR; stdcall;

    BSTR str;
    typedef BSTR (__stdcall* GetLastErrText_funtype)();
    str = (GetLastErrText_funtype)GetLastErrText(); // <<<<<<<< ОШИБКА
    std::cout << "\nstr = " << str;

BSTR bstr = (BSTR )((GetLastErrText_funtype) GetLastErrText)();

type
  BSTR = WideString;