Foreign checks posted in a consumer or business checking account are sent to another bank for exchange.
What does that mean; i.e. do you send the checks to another bank via the mail or through the clearing system? When does the customer get credit for the "deposit?"
In short, if the fee is not "in connection with the account" Regulation DD does not require that you disclose it or that you give advance notice of a change.
Assuming that you do not give customers any sort of credit for your receipt of a non U.S. check intended for deposit, I would say any fee is not "in connection with the account."