The fast-growing language learning app is rocking at a time when many learning apps are rolling downhill. Last year taught investors Duolingo's (DUOL 0.05%) love language. Shares of the language learning specialist more than tripled, up 219% in 2023. It's been a different story this year. Duolingo stock is trading 18% lower in 2024, going the wrong way in a rising market. There is still a lot to like in Duolingo. The stock is highly unlikely to triple again in 2024, especially with less than six months to m ...