60% sureLots of sources credit Voltaire with this, and they agree with each other. The book or the speech it first came from hasn't turned up yet.
What turned up
L'Enfant prodigue, Preface (1736): "Tous les genres sont bons, hors le genre ennuyeux." No single named English translator located for this standard rendering; French original + primary work/year confirmed.
Work
L'Enfant prodigue
Occasion
1736
Sources checked
en.wikiquote.orgChecked using claude-sonnet-5, 21 August 2026Sourced section, raw wikitext fetch — French original + citation to L'Enfant prodigue preface, 1736
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