Duolingo is a superb site for learning languages, and it's self-funded by crowdsourcing translations. I'm impressed.
miniblog.
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Modelling foreign language learning in the Duolingo app by fitting a machine learning model! When you have millions of users you can measure recall effectiveness with a high degree of confidence:
@duolingo should there be a translation visible on a sentence's discussion? Found whilst doing http://t.co/cFmBVS2RaA http://t.co/QcoGZxyVSQ
