procedure SetRU;
var
  Layout: array [0.. KL_NAMELENGTH] of char;
begin
  LoadKeyboardLayout(StrCopy(Layout, '00000419'), KLF_ACTIVATE);
end;

procedure SetEN;
var
  Layout: array [0.. KL_NAMELENGTH] of char;
begin
  LoadKeyboardLayout(StrCopy(Layout, '00000409'), KLF_ACTIVATE);
end; 

или

var
  rus, lat: HKL;

rus := LoadKeyboardLayout('00000419', 0);
lat := LoadKeyboardLayout('00000409', 0);

SetActiveKeyboardLayout(rus);