May a zimun be made with 3 men when one of them is unable to respond properly to the zimmun (because he can’t read hebrew or doesn’t understand how to make it, etc.) Someone could theoretically help the person along however the shailo as it is with the person that can’t respond what would be the din?
Even if he doesn’t know how, a zimun is made, and he listens.
The reason for this is that having eaten together, the group is obligated in zimun, and the obligation stands even if one of the group doesn’t know how to answer. They others do the zimun for him, and he listens.
See Betzel Ha-Chochmah 5:78; Be’em Moshe 5:94; Yaskil Avdi 8:27; Minchas David 4:17-22.