Which language learning app first implemented an adaptive AI system that customizes lesson difficulty based on individual user performance patterns?

The language learning industry has been transformed by AI and machine learning in recent years. Major players are investing heavily in natural language processing technologies to create more intuitive, personalized learning experiences. But how well do you know the key product innovations that have shaped this rapidly evolving market? Test your knowledge of the companies and technologies driving change in language education software.

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Duolingo with its BERT-based personalization engine (2019)
Babbel with its Neural Adaptation Framework (2020)
Rosetta Stone with its Adaptive Recall™ technology (2018)
Memrise with its MemAI learning algorithm (2021)