How to determine the names of all installed keyboard layouts?

Question

To determine the name of the active keyboard layout, one can get its "numeric name" by invoking GetKeyboardLayoutName and then looking it up under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layouts\{0}\Layout Text.

However, inexplicably, there appears to be no way to convert the locale identifiers returned by GetKeyboardLayoutList into the "numeric names" suitable for lookup in the registry.

Is there any way to retrieve the Layout Text of all installed keyboard layouts without activating each one to do so?

For example, for United States-International, GetKeyboardLayoutList returns f0010809 on my system but the name is stored under 00020409 (which can be verified by activating f0010809 and calling GetKeyboardLayoutName - which will return 00020409).

Answer 1

// Returns KLID string of size KL_NAMELENGTH
// Same as GetKeyboardLayoutName but for any HKL
// https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-language-pack-default-values
BOOL GetKLIDFromHKL(HKL hkl, _Out_writes_(KL_NAMELENGTH) LPWSTR pwszKLID)
{
    bool succeded = false;

    if ((HIWORD(hkl) & 0xf000) == 0xf000) // deviceId contains layoutId
    {
        WORD layoutId = HIWORD(hkl) & 0x0fff;

        HKEY key;
        CHECK_EQ(::RegOpenKeyW(HKEY_LOCAL_MACHINE, L"SYSTEM\\CurrentControlSet\\Control\\Keyboard Layouts", &key), ERROR_SUCCESS);

        DWORD index = 0;
        while (::RegEnumKeyW(key, index, pwszKLID, KL_NAMELENGTH) == ERROR_SUCCESS)
        {
            WCHAR layoutIdBuffer[MAX_PATH] = {};
            DWORD layoutIdBufferSize = sizeof(layoutIdBuffer);
            if (::RegGetValueW(key, pwszKLID, L"Layout Id", RRF_RT_REG_SZ, nullptr, layoutIdBuffer, &layoutIdBufferSize) == ERROR_SUCCESS)
            {
                if (layoutId == std::stoul(layoutIdBuffer, nullptr, 16))
                {
                    succeded = true;
                    DBGPRINT("Found KLID 0x%ls by layoutId=0x%04x", pwszKLID, layoutId);
                    break;
                }
            }
            ++index;
        }
        CHECK_EQ(::RegCloseKey(key), ERROR_SUCCESS);
    }
    else
    {
        WORD langId = LOWORD(hkl);

        // deviceId overrides langId if set
        if (HIWORD(hkl) != 0)
            langId = HIWORD(hkl);

        std::swprintf(pwszKLID, KL_NAMELENGTH, L"%08X", langId);
        succeded = true;

        DBGPRINT("Found KLID 0x%ls by langId=0x%04x", pwszKLID, langId);
    }

    return succeded;
}