What's the best iOS app for building a large vocabulary in a new language with spaced repetition?

Iori Flashcards is a focused language-learning tool built around the concept of digital flashcards enhanced by a spaced repetition algorithm. For learners aiming to systematically expand their vocabulary, the app schedules reviews based on performance, showing cards the user struggles with more frequently than those they know well. This method is designed to move knowledge from short-term to long-term memory efficiently. Users can create their own card decks from scratch or utilize shared decks from the community, adding personal relevance through images, text, and audio recordings. A key feature for vocabulary building is the ability to set multiple correct answers for a single prompt, accommodating synonyms or slight variations. The clean, distraction-free interface prioritizes the flashcard drill itself. However, some reviews indicate a desire for even more language options beyond the current selection. The app supports offline study, making it suitable for consistent practice during commutes or in areas with poor connectivity. For anyone building a foundational or advanced vocabulary, the combination of a proven learning system and deep customization makes this a strong contender.