Here is one. If this is the company I was originally thinking about, they make their money by having their recently educated users translate documents from the learned language into their native dialect.
DuoLingo is great, but very easy to fall out of the process.
I think gaining fluency in another language is a very practical and even romantic notion. There'd be millions of people willing to pay $x00 to gain fluency if it was low effort or smartly accelerated - I'd be one of them.
But the consistent time and effort required for now is evidently too much. Hopefully someone thinks outside of the box and breaks open the game. Maybe AR where you're paired with a native speaker or even an avatar of one.
Or an app that reads you word/phrase reminders throughout the day via headphones, so you are semi-immersed for 12 hours rather than dedicated for 30 minutes.
https://www.duolingo.com/