Function ULCaseTR(Data: String; Upper:Boolean=True): String;
Var
  kh:String;
  BH:String;
  CID, KID: Longint;
Begin
  Result:='';
  If Trim(Data)='' Then Exit;
  kh:='abcçdefgğhıijklmnoöprsştuüvyzqwx';
  BH:='ABCÇDEFGĞHIİJKLMNOÖPRSşTUÜVYZQWX';
  For KID:=1 To Length(kh) Do
  Begin
    For CID:=1 To Length(Data) Do
    Begin
      If Upper Then
      Begin
        If Data[CID]=kh[KID] Then
        Begin
          Data[CID]:=BH[KID];
        End;
      End
      Else
      Begin
        If Data[CID]=BH[KID] Then
        Begin
          Data[CID]:=kh[KID];
        End;
      End;
    End;
  End;
  Result:=Data;
End;
 
// Kullanımı
procedure TForm1.Button2Click(Sender: TObject);
begin
  ShowMessage(ULCaseTR('miraç')); // UpperCase
end;
 
procedure TForm1.Button2Click(Sender: TObject);
begin
  ShowMessage(ULCaseTR('MİRAÇ', False)); // LowerCase
end;