This is really version 2 of an app that I have been working on for a long time. There's no vocabulary app built natively for iOS, so I built one, with swiftUI.
No personal data of any kind is collected. All that is saved is the actual cards and lists in CoreData, stored in iCloud with CloudKit.
Open source: Github
Email me at email@example.com
Words are arranged based on lists and sublists. The Library is the root list, In which you can add cards directly, or add sublists, which can have sublists of its own. This solves the problem of having only folders that can only store lists, or lists that can only store words.
When this feature is enabled, instead of only showing the words in this current list, all words inside the sublists are also shown. This allows for further organization into sublists, while preserving the ability to review everything at once.
When sorting by date or familiarity, the sorting changes instantly, what I find myself doing most often is sort by oldest first, and, just checking off each of the cards. The cards will slide to the bottom of the list and the next one will slide up.
Instead of a separate view for quiz modes or flash cards, there's just view options for each of the cards: Full, Words only, or Definition only. You can tap on each of the cards to flip it one by one. The benefit of this is that your sorting options get preserved, and you can scroll around much easier than swiping to the next flashcard, for example.