If you're looking for something free and easy and convenient to learn a language, there's always Duolingo:
Jay Doubleyou: duolingo: free language-learning app
It works because it makes learning into a game:
Jay Doubleyou: gamification in learning
What works about it is that it focusses on input:
Jay Doubleyou: "focus more so on input & absorbing the language"
Which is what many say is the right approach:
Jay Doubleyou: to acquire a language you need lots of comprehensible input
But it's not perfect:
Jay Doubleyou: the limitations of language apps
You can make it part of a mix:
Jay Doubleyou: creating your own little online language course
Or you can improve it:
Jay Doubleyou: how to make duolingo work
Or you can simply walk away:
Duolingo Sucks, Now What?: A Guide
Now that the quality of Duolingo has fallen (even more) due to AI and people are more willing to make the jump here are just some alternative apps and what languages they have:
"I just want an identical experience to DL"
Busuu (Languages: Spanish, Japanese, French, English, German, Dutch, Italian, Portuguese, Chinese, Polish, Turkish, Russian, Arabic, Korean
"I want a good audio-based app"
Language Transfer (Languages: French, Swahili, Italian, Greek, German, Turkish, Arabic, Spanish, English for Spanish Speakers)
"I want a good audio-based app and money's no object"
Pimsleur (Literally so many languages)
Glossika (Also a lot of languages, but minority languages are free)
*anecdote: I borrowed my brother's Japanese Pimsleur CD as a kid and I still remember how to say the weather is nice over a decade later. You can find the CDs at libraries and "other" places I'm sure.
"I have a pretty neat library card"
Mango (Languages: So many and the endangered/Indigenous courses are free even if you don't have a library that has a partnership with Mango)
Transparent Language: (Languages: THE MOST! Also the one that has the widest variety of African languages! Perhaps the most diverse in ESL and learning a foreign language not in English)
"I want SRS flashcards and have an android"AnkiDroid: (Theoretically all languages, pre-made decks can be found easily)"I want SRS flashcards and I have an iphone"AnkiApp: It's almost as good as AnkiDroid and free compared to the official Anki app for iphone"I don't mind ads and just want to learn Korean"
lingory
"I want an app made for Mandarin that's BETTER than DL and has multiple languages to learn Mandarin in"
ChineseSkill (You can use their older version of the course for free)
"I don't like any of these apps you mentioned already, give me one more"
Bunpo: (Languages: Japanese, Spanish, French, German, Korean, and Mandarin)
#EDIT: Added a great resource for ESL and African languages that weren't found elsewhereDuolingo Sucks, Now What?: A Guide – @ruhua-langblr on Tumblr
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