1) It seems to me that digital language learning cannot be permanent. Specifically, I once tried to learn Japanese through a special app, I really lack a teacher who will correct and say that you are doing it wrong.
2) A difficult question, because different languages have different rules and some of them may not even have words that mean something. Even with face-to-face learning, people who speak differently will not be able to completely overcome cultural differences, and even more so digitally, because they cannot even contact each other.
3)To develop self-motivation, you need to encourage yourself. For example, if you somehow advance in the language you are learning, you can play your favorite game for a while or watch a movie