This is a very interesting article from 2012, that looks at how Memrise’s design was inspired by the Facebook game, Farmville, and how co-founder Ed Cooke planned to deal with the rampant cheaters on the site at the time, and further gamify the Memrise experience in the future.
thanks!
unfortunately, the question (in the title) remains unanswered in fact … the only hint was “more gamification” - memrise did this, but the cheating just got even wilder… so, the team took finally out the main cheating incentive (probably), the so called “globalleaderboard” 
(a pity that the article did not address the main question, “how to learn better and faster”)
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