I would argue that some advanced questions should be asked (and discussed) in Russian, not English.
For example, this one
This is based on the guess that there are two distinct groups of participants: People who study Russian as a second language and can't yet read it comfortably. They do not need these advanced questions, they'll only be confused by those. You can't understand or answer this question without a long history of reading texts in Russian.
And people who can understand or answer this question can also read Russian without many problems, or they are native speakers. So it makes no sense NOT to discuss the question in Russian, since it removes some impedance mismatch and, to say it humbly, is easier on native Russian speakers.
What do you think? Is there a policy on that?