If you truly want to learn a language, no singular app will work. You need to find a good curriculum for your language for grammar. Typically this means taking

If you truly want to learn a language, no singular app will work. You need to find a good curriculum for your language for grammar. Typically this means taking a class or buying a good textbook. Sometimes you get lucky and find a comprehensive website. For audio / speaking practice, I recommend glossika. It’s like a modern version of pimsleur. For vocabulary I recommend Anki. I have used that for the last two years and written about it. Generally you can start with a premade deck and eventually make your own once you’re a little bit more advanced in the language. For talking to people, try HelloTalk. You can make posts and natives can correct them, and you can have conversations with native speakers. Once you are intermediate or advanced+, you need to start consuming native material. Try searching on YouTube, or look for graded readers. Searching reddit about recommended textbooks / etc is usually useful, depending on how popular your language is.