[whatever_dude]

For non-ubiquitous languages (everything other than English), part of the difficulty of learning is not just the basic learning, it's retaining what you've learned; it might be difficult to practice it unless you're on the country that speaks it. Of I'm in the middle of Tennessee, probably don't have a lot of opportunity to prescribe my Japanese. That's where Duolingo shines, in my opinion: as a learning companion.