Learn languages by playing a game. It's 100% free, fun, and scientifically proven to work.
I have a solid grasp of the language I am studying. Duo provides me with a chance to practice my speaking skills, but I must be cautious to respond exactly as Duo expects. If I make a mistake when practicing with Duo, the discussion points do not always refer back to that mistake. This is frustrating. Additionally, the accents of the small child and grumpy old man are distracting; they detract from my ability to practice effectively.