As per the subject. I see duolingo is mostly about translation from German, which is good, but I'd like to practice the other way round. I also speak Spanish if that helps.
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You could always try using Lang-8. Many people include a copy of the text in their native language in case any part is particularly incomprehensible. So you could always translate a text into German, post it and attach the original English (or Spanish). Also, I'd tell people it's a translation and see if they'd critique it. I don't know it that'll work, but it's worth a shot.
Wikipedia has a category with similar websites. Sadly, I cannot give any information on their quality.