Evne Apple has discovered this. Of course they still implement at-will employment and they pretty much exclusively hire people from their Scientology contracting partner - I am surprised no one in Sweden has caught on to them.
To be honest I don't really think it is that hard.
For children it is a question about survival. They practice every time they open their mouth and try to communicate. 24 hours a day 7 days a week. If you did this for 6 months with lets say Chinese, I am sure you would pick it up very fast.
Adults have an advantage over children, I would even say. They already speak one language and have reference points already.