To disfranchise someone is to take away their right to vote, or sometimes other rights of a person in a country. It is a politics and law word, not a kitchen-table word. You will hear it about history (who was not allowed to vote), about unfair rules, and about people in prison. Though actually, most people now say disenfranchise, which means the same thing and is far more common; disfranchise sounds older and a little stiffer. The piece franchise here is the old idea of a public right, not the shop sense (a McDonald’s franchise). Same family of meaning at the root, different life in modern English. Ordinary speakers more often say “they took away his right to vote.” Who says it: courts, textbooks, political writing.

剝奪選舉權、剝奪投票權（台灣法律上相近、但範圍更廣的處分叫「褫奪公權」）