"War is Peace" is doublespeak; an inherent contradiction. Anybody can say it and still see the contradiction and believe that it isn't true. Doublethink is the internalization of that doublespeak. A Party member says it and sees no contradiction. Deep in their hearts, they understand that to be in a never ending war is to experience neverending peace.
All that to say that doublespeak was certainly a thing in the novel, as it labours on the distinction between doublespeak and doublethink.