Which linguistic principle was primarily used in naming Duolingo's gamified language learning platform?

In the world of language learning and linguistics products, marketing teams carefully craft product names using specific linguistic principles to appeal to their target audience. This naming process combines psychology, cultural awareness, and linguistic expertise. How well do you know the strategies behind naming language learning products and tools?

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Phonaesthetics (the pleasing sound of repeated 'o' vowels for global appeal)
Portmanteau (combining 'dual' and 'lingo' to represent bilingual learning)
Eponymy (named after founder Luis von Ahn's childhood nickname)
Onomatopoeia (mimicking the sound of conversation between two people)