There are several archaeological bilingual and multilingual artefacts, e.g.
- the Philae obelisk (ca. 118 BC?),
- the Rosetta Stone (196 BC; Ancient Egyptian hieroglyphs, Demotic script, and Greek script),
- the Ezana Stone (4th C BC; Ge'ez, Sabaean, Greek),
- the Behistun Inscription (6th/5th century BC; three different cuneiform script languages: Old Persian, Elamite, and Babylonian),
- the Karatepe Bilingual (8th century BC; Phoenician language and Luwian language hieroglyphs).
We also know from, e.g. Pliny the Elder's Natural History, that classical antiquity produced a few polygots.
But what are the oldest documented language learning techniques or resources? (I am not referring to the multilingual artefects listed above, since these were not originally intended as learning tools.)