TOPIC:

//----------------------------------------------------------
// special character
//-----------------
//ö = #246
//ä = #228
//ü = #252
//Ö = #214
//Ä = #196
//Ü = #220
//ß = #223
//----------------------------------------------------------
procedure TfrmLogIn.txtBenutzernameKeyPress(Sender: TObject; var Key: char);
begin
  if Key = #13 then
    txtPasswort.SetFocus
  else if not (Key in [#8, ' ', '_', #246, #228, #252, #214, #196, #220, #223, 'a'..'z', 'A'..'Z', '0'..'9']) then
    begin
      Key := #0;
      Beep;
    end;
end;

procedure TForm1.txtPasswortUTF8KeyPress(Sender: TObject; var UTF8Key: TUTF8Char);
var
  myKey   : char;
  myUTF8  : utf8string;
  myANSI  : ansistring;
begin
  myUTF8  := utf8key;
  myANSI := lconvencoding.UTF8ToCP1252 (myUTF8);
  if (length(myANSI) = 1) then
  begin
    myKey := myANSI[1];

    if myKey = #13 then
       Application.MessageBox('Enter', '', 0)
    else if not (myKey in [#8, ' ', '_', #246, #228, #252, #214, #196, #220, #223, 'a'..'z', 'A'..'Z', '0'..'9']) then
      begin
        UTF8Key := #0;
        Beep;
      end;
  end;
end;