I'm a native speaker of Russian, and I can't guess Duo's pattern either. :D
She doesn't HAVE to use the Russian language when speaking about Russian. Based on your response, sorry if my message for some reason came off rude, but I was just stating that you may have been misunderstood. Even if I was misunderstanding, there is no reason for you to use умник. If anything you're one.
Look at the original comment:
"With whom is this man standing?" - surely? Always remember, never use a preposition to end a sentence with.
This sentence is clearly referring to the English language. If it had been written in Russian, or if the phrase "in Russian" or any other language had been used in the sentence, then that would have signified it's reference to that language.
You are knocking me for using «умник», yet you are the one who called me "smarty" first. Get a grip, homie.
This is antiquated English and as it is translated here, sounds awkward. If insisting on using 'whom' however, it would more likely be constructed; With whom is this man standing? Otherwise common English would drop the 'whom' and simply go with "Who is this man standing with?" Here is a fun little excercise to practice your who v's whom sentences: http://www.bristol.ac.uk/arts/exercises/grammar/grammar_tutorial/page_61.htm#whomex