Two computers, A is trusted and B is untrusted. B is networked and hooked up with the rest of your system, A is in a vault and completely air-gapped. A has your wallets.

Give both a printer and webcam/scanner to both. B prints a transaction encoded as a QR Code (or something custom, if those don't hold enough data?) as well as key details (transaction amount say) in giant black bold capitalized English.

The human operator checks the english description for sanity, then gives it to computer A. Computer A reads the QR code, does OCR to confirm the key details (or lets the operator confirm them on the screen) and the QR code match, and preforms the transaction.

This could work at a "local bank branch scale" I think, but getting it up to "website scale" would be... improbable.

Not sure if I would trust this with my money, but it would be fun to implement.

(technically A wouldn't be air-gapped, it would just be operating over a QR-code sneakernet.. Should be reasonable though I think.)

IIRC, it's possible to create a one-way TP cable. Might be a little more feasible :)

There's a flaw in your system right there.

Lots of industrial accidents and accidents with computers have been from stupid operators (rather than buggy code per se).