Hi Issam,

Start with this code and let me know how it works. Try both nDlgType values
nDlgType = BITOR(MB_RTLREADING, MB_RIGHT, 64)
and then
nDlgType = BITOR(MB_RTLREADING, 64)

#DEFINE MB_RTLREADING 0x00100000
#DEFINE MB_RIGHT 0x00080000

DECLARE INTEGER MessageBoxW IN user32 As MessageBoxAPI;
	INTEGER hWindow, STRING lpText,;
	STRING lpCaption, LONG uType

LOCAL cMessage, cCaption, nDlgType
TEXT TO cMessage NOSHOW PRETEXT 4
Adding two right-to-left marks (RLMs), represented by Unicode 
formatting character U+200F, in the beginning of a MessageBox 
display string is interpreted by the Win32 MessageBox rendering 
engine so as to cause the reading order of the MessageBox to be 
rendered as right-to-left (RTL).
ENDTEXT

cMessage = ToUnicode( m.cMessage )
cCaption = ToUnicode( VERSION() )

nDlgType = BITOR(MB_RTLREADING, MB_RIGHT, 64)
*nDlgType = BITOR(MB_RTLREADING, 64)

= MessageBoxAPI(_screen.HWnd, m.cMessage, m.cCaption, m.nDlgType)

FUNCTION ToUnicode(cStr As String) As String
RETURN STRCONV(m.cStr+CHR(0), 5)

This article may contain some useful information too:
http://www.microsoft.com/middleeast/msdn/ArabicCalendar.aspx