Anki is an offline-first flashcard program that I use along with other methods.

• Pimsleur language learning ( learn at instinct-level, not the prompted-stuff or memorizations that many other language trainings work at )
• Tandem app ( probably not great for privacy, been awhile since I tried it ), you help someone learn your language, & they help you learn the target language one you want
• simplified short-stories, books of collections of the things..
• TV in the target-language
• songs because they wire-up your other-hemisphere ( right-hemisphere for the 85% of people who have language in the left ) with the language, & that reinforces the language's patterning
• flashcards for the stuff that actually requires you to remember specific arbitrary things, like difficult words, or whatever, for random moments throughout the day

Some of this I got from a book by a guy who knew .. 29 or something? .. languages & worked for the CIA.

Other stuff ( songs ) from science news, & my discovering that language-destroyed-by-stroke people could sometimes still communicate through picking a song which had the idea they were trying to communicate..

I have a bad time learning anything through hearing, though, so .. language-learning seems itself to be kinda broken ( I learned English before anything, & it was my 2nd wave of braindamage which took much learning from my life, not the autism 1st-wave ).

These are the best tools I know-of.

I wish I could learn languages.

I wish everybody learned other-languages, to understand just how diverse humankind's meanings can be..

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The fastest way to learn a language is with the comprehensible input method. You watch videos, all of which are 100% in the target language. The early videos are easy, involving simple things, and using props and gestures to provide the context for understanding. As you learn more, the videos progress and become more difficult. It's amazing how quickly you pick up things and retain them. There is a lot of comprehensible input material for Spanish, French, and English, but you can use children's television shows like Peppa Pig where there isn't specific material for the target language. Here is a beginner video in Spanish.

Date a native speaker of that language for a while.

A book you get from your local library.

You can try Language Transfer

It’s completely free. Free (and ad free) iOS or android app, free audio file downloads. There’s also a course on music theory.

Find a local special interest group that gets together to practice. Check meetup.

A book with CDs to listen to.

Try to decide what your threat model is. A language learning app (except harvesting traditional device id and such) doesn't reveal very important info to anyone.

The only know which language you learn and your approximate level. Sure that's better if there's a more private way of doing it, but the core principle of learning a language doesn't reveal very much.

You can also try to find some kids shows in the language you're interested in. I'm sure sesame street has been dubbed into many languages by now.

I have a suggestion that is not FOSS, but it is privately held so the pressure to be profitable each quarter is not at all the same as publicly held companies.

Check out the privacy policies of LingQ and Rosetta Stone. Idk if they’re good, but I know they’re the most efficient language-learning apps right now. They require the least amount of minutes using them to achieve the highest scores in standardized language tests.

fmhy.net should have resources

If you want to learn Japanese, I can highly recommend KanaDojo.

Buy a book and learn with a compiler that was built before the spy craze.

Babel mini app in delta chat ;p

📖+✏️🗒️+👂+👄

Anki with deck cards already made, for vocabulary. Youtube video to train sentences (type : easy + name of the language)