Notes from for LitNerd (YC S21) re: IPA, "Duolingo's language notes all on one page", Sozo's vowel and consonant videos, Captionpop synced YouTube videos with subtitles in multiple languages,: https://news.ycombinator.com/item?id=28309645
Spaced repetition and Active recall testing like or with Mnemosyne or Anki probably boost language retention like they increase flashcard recall: https://en.wikipedia.org/wiki/Anki_(software)
ENH: Generate Anki decks with {IPA symbols, Greek letters w/ LaTeX for math and science, Nonregional (Midland American) English, }
Google translate has IPA for some languages.
"The English Pronunciation / International Phonetic Alphabet Anki Deck" https://www.towerofbabelfish.com/ipa-anki-deck/
"IPA Spanish & English Vowels & Consonants" https://ankiweb.net/shared/info/3170059448