With 25 million monthly active users, Duolingo has become an immensely popular language-learning app, for good reason. It offers free instruction in 31 tongues, and it’s genuinely fun, with whimsical cartoon characters teaching sometimes-hysterical phrases that keep learners entertained. (Fans have compiled lists on Twitter and Tumblr .) One of my favorites, from German, translates to “They are washing the holy potato.”

But until today, users have seen only part of the material the service had created, much of which it wasn’t actually presenting in the app. “I would say we were throwing out at least half of our content completely,” says Karin Tsai, the engineer who oversaw its new revamp. “Some sentences and exercises were just way too hard for users at the beginning level.” With its update, called Skill Levels, eager students have the option to do more-complex exercises, even from day one. Duolingo also announced that it’s working on additional exercises, such as reading and listening comprehension, that will roll out later this year.

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The app follows the common structure of teaching ever more advanced skills, starting with basic words and phrases like “Je suis un garçon,” and working up to complex topics like business and religion. In the past, if a skill section had been too long or complex, people would have gotten frustrated and dropped off. The new design gets around the problem by offering five levels for each skill, designated by crown icons. Students have to complete only the first level to move on to new skills; but if they want more practice on, say, the Spanish passive voice, they can now get it.

I tried the system in German, which I know well, and French and Spanish, in which I’m abysmal. Skill Levels solves one of my biggest language-learning problems: I forget stuff. (Perhaps I’m not alone.) Instead of having to go back over old exercises to refresh, say, my knowledge of Spanish food names, I can try a new level in that category, with new exercises and funny phrases, that reenforce the material.

I can also push myself with more complex sentences and combinations of skills that teach those words or grammatical constructs. Before, Duolingo mostly asked users to translate sentences into the language they already knew because it was easier, for instance. Now they have more opportunities to practice translating in both directions if they choose to keep leveling up.

In December, Duolingo quietly seeded the new version of the app to a sampling of users, some of whom wrote excellent tutorials on the company’s message board. Despite confusion among some users, the results have been good overall, according to Tsai, with people spending more time on their language. “They are speaking it and writing it a lot more than they used to,” she says.