The most important thing in learning a language is not knowing a bunch of rules and new words, but understanding what people are saying and being able to quickly and precisely formulate your thoughts to maintain a conversation.
And that takes a lot of practice.
— Flying to another country? Expensive and too hardcore for the vast majority of people.
— Language exchange? Cheap, but finding a good conversation partner is quite a challenge. Not to mention that talking to a stranger in a foreign language is an insurmountable psychological barrier for many.
— Tutor? Effective, but you have to fork out if you want significantly enhance your language skill.
The solution is an AI tutor. Effective, cheap, available whenever you can be online and would like to speak.