I suppose they created these terms to make the difference between illiterate people as found in Western countries despite compulsory education, and "primitive" tribes with no writing system of their own, but with an elaborate system of oral transmission of knowledge, traditions and mythology. Ethnologists' concern is to have precise scientific terms that are not tainted with prejudice.A quick google search confirms that you are right, Qcumber. I stand corrected.
Je voudrai traduire "unlettered people". J'hésite entre 'illettré" et "sans écriture".
J'ai vu que "sociétés sans écriture" pouvait se traduire par "oral societies". Aurait-on pu traduire par "unlettered societies ?