It really isn’t clear what you are asking. Are you saying that you are doing something in accordance with the contract? Are you proposing to change the contract? Are you raising an issue that wasn’t anticipated by the contract? I don’t think “incurred” is the right word, or is being used correctly here. You incur costs by doing something. We incurred unanticipated translation costs and are passing them on to you. We incurred unanticipated translation costs due to your requests and are passing them on to you. We are passing these costs on to you as the contract requires. (Explain. Perhaps the contract allows reimbursement for expenses.) We are passing these costs on to you as discussed. We trust you will not object to reimbursing us for the additional translation costs.

This is probably better : "I would like to notify you that a translation fee will be incurred, in addition to the contract fee." Or even "I would like to notify you that an additional fee will be incurred, to cover unanticipated translation costs."