Defining whether the current system locale is RTL or LTR - c++

Question

We develop a Windows API app where there is a context menu with nested submenus. We localize the app in several languages, including Hebrew.
As keyboard support is a must for us, we need to know whether the submenu should be opened upon right arrow (LTR) or left arrow (RTL) keypress.
Our developer does use the TrackPopupMenu() function described here on MSDN, but he needs to know when to set the TPM_LAYOUTRTL flag.
So the question is: how to define whether the current system locale is LTR or RTL to handle the menus properly?

Answer 1

I'm answering since we have found a solution (and a comment confirmed we are on the right way).
In order to define whether the current system locale is RTL or LTR, we should use GetLocaleInfoEx with LOCALE_IREADINGLAYOUT. MSDN says the following about it:
Windows 7 and later: The reading layout for text. Possible values are defined in the following table.
Possible values actually are:
0 — left-to-right (as in English);
1 — right-to-left (as in Hebrew or Arabic);
2 — Either read vertically from top to bottom with columns going from right to left, or read in horizontal rows from left to right (as in Japanese);
3 — Read vertically from top to bottom with columns going from left to right (as in Mongolian).

Answer 2

We use the following in-house code:
bool IsCurrentInputLanguageRTL ( void )
{
bool ret=false;
auto layout = GetKeyboardLayout(GetWindowThreadProcessId(GetForegroundWindow(), NULL));
auto lcid=MAKELCID(LOWORD(layout),SORT_DEFAULT);
LOCALESIGNATURE localesig;
// Windows XP and higher.
// Unicode subset bit fields: https://msdn.microsoft.com/en-us/library/windows/desktop/dd374090(v=vs.85).aspx
// Bit 123: Windows 2000 and later - Layout progress, horizontal from right to left.
if(GetLocaleInfoW(lcid,LOCALE_FONTSIGNATURE,(LPWSTR)&localesig,sizeof(localesig)/sizeof(WCHAR)) != 0)
ret = (localesig.lsUsb[3] & 0x08000000)!=0;
return ret;
}