The council is making no visible progress, save for a lot of talk going on behind closed doors.

의역입니다만 "협의체"에 대한 부정적인 맥락에서 위와 같이 번역해 봤습니다.

While 밀실 could be interpreted in some different ways including closed-door which majorly stand for the meaning that the event is going on out of public sight, there are some factors to be considered for the term in the sentence and the context.

The first is the structure of the sentence, as consultation is exploited to emphasize the function of consultative group, the following term must mean the contrary, which would imply lack of such a consultation and while considering that the word is characterized by openness and transparency of the process in the group as well as in society, 밀실 should be the exact antonym against those two factors, but while containing implication of negotiation.

And the context is here, as second, that negotiation in the second phrase will have deteriorated nature compared to first one as it is author's intention. It means the term to be used could be 'closed-door' as one standard and literal translation of 밀실, however eventually falls into neutralized area on positivity-negativity scale, or spectrum, then it wouldn't fully express the meaning of source text.

Finally it seems certain that the term should have strong negativity seen by public view and only one that can be found to be appropriate will be 'Backroom'. As Back- has been used in English to show implication of possibility of corruption and inappropriateness and impropriety of actions, and with customary use of the term especially aiming at Asia's unique politics culture firstly known to the world by Japan's political custom rooted in their history, and then it is very easily presumed that the Korean application of the term 밀실 is the same one of Japan as Korea's modern politics has been under big influence of the country especially when the term is adopted.

While considring all of above reasons, the final term Backroom discussion would be drawn for best suggestion. (Thank you for reading.)