However, here are some ways you could convey a similar meaning in French, depending on the context:
If you want to express that someone's hopes are unrealistic:
* "Rêve un peu!" (Dream a little!) - This is a playful way to say that someone is dreaming too big.
* "Tu rêves !" (You're dreaming!) - This expresses disbelief and implies that what the person is hoping for is impossible.
* "C'est pas réaliste !" (It's not realistic!) - This is a more direct and assertive way to say that someone's hopes are unrealistic.
If you want to express that someone is naive:
* "Tu es naïf(ve) !" (You're naive!)
* "Tu te fais des illusions !" (You're fooling yourself!)
* "Tu te laisses bercer par des chimères !" (You're letting yourself be lulled by chimeras!)
If you want to express that someone is being delusional:
* "Tu es complètement à côté de la plaque !" (You're completely off the mark!)
* "Tu te fais des idées !" (You're getting ideas!)
* "Tu es dans ton monde !" (You're in your own world!)
Remember that the best way to express yourself in French depends on the specific situation and your relationship with the person you are speaking to.