Crime type - we are talking about local Chinese criminal law.[/i]
"Chinese criminal law" does not apply here. The Bitcointalk.org forum falls under US jurisdiction.
And it is absolutely possible that two or more people living in the US, speak Chinese, so even on this forum they prefer to communicate in Chinese (native) rather than in English or another language.
It's fascinating how scared people are, they expect the Chinese authorities to search for them around the world because they participated in the discussion about the "forbidden".