Duolingo (DUOL 1.17%) operates the world's most popular digital language education platform, and the company continues to deliver stellar financial results. Duolingo is elevating the learning experience with artificial intelligence (AI), which is also unlocking new revenue streams that could fuel its next phase of growth.Duolingo stock set a new record high in May, but it has since declined by 26%. It's trading at a sky-high valuation, so investors might be wondering whether the company's rapid growth warra ...