Improve English writing skills
I do some writing at my job (English). Recently, I started noticing that my writing skills were rapidly improving. My coworkers noticed, also. I was delighted with myself, but then it hit me...translating every day on Duolingo is the reason for the improvement! An unexpected bonus! Thank you so much!
Learning an new language is a big plus when people begin to pay attention to subject/verb agreement, learn the difference between adverbs and adjectives, and the like. And we have people here that complain when Duo does not accept "gonna" and say that 'my mother loves him and me' is "bad grammar!"
I feel the same, too, but mostly because of posting and commenting on discussions. For 9 months I've been learning French and German using courses for English speakers and I feel that my writing in English becomes significantly more fluent (I am not a native speaker).
Doing translations is definitely good for improving language skills. I know because I am a translator :-)
There is a global movement for writing that is clear and easily understandable to the user. When I translate or vote on Duolingo translations, I think, "Is this simple, clear, and brief? Could we eliminate extra words while retaining the flavor of the original? Could the majority of people understand this?" (See Wikipedia: Plain Language Movement, Plain English, and the U.S. Writing Act of 2010.)