Subtitles to Flash Cards Program
Though I've not used Duolingo, I have learned Japanese and one important tool for fluency was a program called subs2srs (subtitles to spaced repetition software aka electronic flashcards).
The basic idea is that subtitles have a sentence, a start time and a stop time that tells the video program to display the sentence. In most cases, the subtitle corresponds with what's being said on the video.
The subs2srs program takes an audio clip from the start and stop time (audio sentence), a snapshot of the video at the midpoint of that time (visual reference), and the actual subtitle itself to generate an electronic flashcard. Instead of audio, it could also generate a video clip or gif from the start and stop time for better reference. A 60 minute TV show then could create 700 or so flashcards for a student to use.
The gives the student a powerful learning tool. Her job would be to understand sentence by sentence the entire hour long program. She is not so much translating as much as comprehending the sentences. As these are electronic flashcards, she can add notes and definitions to clarify the meaning that she can reference during the memorization review.
I think this can be incorporated with Duolingo's group sourced translation project. Instead of just articles, Duolingo can incorporate actual TV shows for users to translate as they're learning the language. These can be legitimate dramas or movies that are entertaining. This means students can be learning from relevant pop culture and not dry educational videos with poor acting and plot.
In addition, the difficulty of the show is easy to determine by tracking which vocabulary is used in the subtitles overall. Once a student's base vocabulary and grammar exceeds the determined difficulty of a video, it can be given to the student to translate.
Again, I used this to full effect when I learned Japanese. What I discovered is that I could follow along with the Japanese show using Japanese subtitles or no subtitles at all. The time at the beginning was about 10 hours of study per 1 hour of drama to comprehend. Later, this time requirement dropped as my grasp of the language increased. In addition, as I listened to mp3's of the dramas on my iPod almost all the time, I found my listening and speaking fluency increased when reacting in real time with Japanese people. Further, my reading speed and comprehension became much better.
I think Duolingo would do its students a great service to find a way to incorporate such a product into its site. From my understanding, the subs2srs is still common license but its also possible to create such a program from scratch. Students that have achieved at least 1,000 vocabulary words will find it a great method for intermediate and advanced study.