The student should be 'completely immersed' in the language from day one.

They leave all contact with the world behind and get completely immersed within themselves.

It closed over his head, and for a moment he was completely immersed.

For the first time since we left Earth, our bodies were immersed completely in water!

So close to the falls, she was completely immersed in the mist.

"After that, I was just completely immersed in pain and grief."

The user becomes completely immersed within the reality of the game.

I made certain that he was completely immersed in the strong brine.

Then he was completely immersed, having left his body far, far behind.

Flow is the mental state experienced by a person completely immersed in an activity.