Ending a sentence with a preposition has a long history in English literature. The technical term is preposition stranding. Check this article from Wikipedia: https://en.wikipedia.org/wiki/Preposition_stranding#Opinions_for_and_against
I hate that Duolingo's English translations are "colloquial," making it hard for students to understand how the Russian and English statements are related (for example: "for whom" and "для кого"). I would give Duolingo an F on many of its English monstrosities ending with "for."
Sure, let's let the masses dictate what should be acceptable English. Are you going to allow "Where is the vegetables at?" Or "I'm going to buy me a jacket." How about "Quiet, I'm laying down to have a rest." and "Them and us was going to the concert."
The English I was taught is what's apparently only spoken in foreign language courses. Now, language students are failing those courses, because they no longer understand standard English parts of speech.