GetKeyboardLayoutName(buffer{:array [0..KL_NAMELENGTH] of Char});
case ((StrToInt('$'+ Buffer)) and $03FF) of
  LANG_ENGLISH: Caption := 'Eng';
  LANG_RUSSIAN: Caption := 'Rus';
end;

ИЛИ

procedure TForm1.Button1Click(Sender: TObject);
var
  AklName: array [0..2] of Char;
begin
  GetLocaleInfo( LoWord(GetKeyboardLayout(0)),
                 LOCALE_SABBREVLANGNAME,
                 AklName,
                 SizeOf(AklName));
  Caption := AklName;
end;