[Faust]

SPOILERS

If you've got a 16 charisma you can bluff Splinter into thinking you already are a sensate. Otherwise, you'll need to join up with the Sensates yourself. All you have to do is tell Splinter you want to become one, and you'll have access to the Private Sensoriums.Unfortunately, I am fairly certain Fall-from-Grace's membership doesn't allow you access. For some reason, only the main character is allowed guest passes.....

To pick up the Dodecahedron, however, you'll actually need to go to living area off the main level of the Festhall. Talk to the clerk, and you'll find out that you have a room from a previous incarnation. The Dodecahedron is in the room. Fiddle with it. It's riddled with some traps that you can avoid with high enough intelligence scores (13 for the first trap, 16 for the second).Otherwise, you'll take some damage. Regardless, you'll eventually find its in an unknown language. Hence, you'll have need of visiting the linguist.

The more I think about, the more I think that doing this might solve your problem with the linguist. Once you have need of finding a linguist, the proper dialogues will become open.