Which packaging design innovation for language learning products led to a 40% increase in sales in Asian markets during the 2010s?

In the world of language learning products, packaging design plays a crucial role in attracting customers and effectively communicating the product's purpose. Different markets around the world have seen various innovative and culturally-specific approaches to language product packaging. This trivia question explores a fascinating case of packaging design adaptation that significantly impacted a language learning product's success in international markets.

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QR codes linking to pronunciation guides spoken by native speakers
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Transparent windows showing physical vocabulary flash cards inside
Magnetic closures that played audio greetings when opened