From my research, the best language learning program is Anki. It is open source and one can make custom 'decks' fairly simply.
Perhaps a dictionary add-on for Anki would be good idea?
I think pretty much the same, to the point where I've committed to save every sentence seen in Duolingo to make then my own Anki deck. I wouldn't bother going back again to Duolingo if I already finished the tree and there are no new units for me.
