yasser, I guess you're using km 1.0x.
Open Edit > Configuration > Menus and scroll down to section 'Encoding' (about line number 140). Add the boldened lines there:
En&coding{
:&Auto Detect
-
macros(ForceCharset(iso-8859-1),&Western (ISO-8859-1))
-
macros(ForceCharset(iso-8859-2),&Central European (ISO-8859-2))
macros(ForceCharset(windows-1250),C&entral European (Windows-1250))
-
macros(ForceCharset(utf-8),&Unicode (UTF-8))
macros(ForceCharset(utf-7),U&nicode (UTF-7))
-
macros(ForceCharset(iso-8859-6),&Arabic (ISO-8859-6))
macros(ForceCharset(windows-1256),A&rabic (Windows-1256))
}
Save your changes and restart km.