"This student is Lukas."
Translation:Dieser Student ist Lukas.
Studierende is the preferred word of many universities since a couple of years, because they want to stay gender neutral, without addressing their students with a long or ugly "Liebe Studentinnen und Studenten", "Liebe StudentInnen" or "Liebe StudentX/*" or whatever. Note that it's only neutral in plural because of the article. Maybe this didn't make its way into foreign language courses yet.
I don't know if duolingo accepts it, but it's perfectly acceptable to use Studierende.
“Studierende” is often used in the plural, to be gender neutral. The problem is, it's gender neutral only in the plural. In the singular, gender is either given away by the article (“der” or “die”) or by the ending—for example nominative “Studierender” (m) or “Studierende” (f).
For this reason, nobody ever uses “Studierende” in the singular form: “Student” and “Studentin” already have it covered.
Just for fun (because I'm tired of this lesson asking us for the exact same phrase over and over) I tried writing "Diese Studentin ist Lukas" and was marked wrong.
I realize Lukas is traditionally a man's name, but with girls now being named Michael or Chris, couldn't this theoretically also be about a woman? There is nothing else in the sentence that determines gender.
Unless my German was wrong? Is that not how you would write the female version?
‘Studentin’ is indeed the correct feminine form. Given, however, how getting new options to be accepted can be a relatively slow process, and reporting this would take time away from working on sentences that really need fixing, I'd suggest leaving this alone (I mean, yes, theoretically you're right, and in a world where Duo had infinite resources I'd like to discuss at length on whether it should or shouldn't be added as an alternative, but this is clearly a speculative translation that no-one would think of intuitively).