Transluceny works differently from any other part of the Poser shader system. Specifically contrary to the general "downstream only" model of the shading system, connecting things to the translucency channel creates "up-stream" effect.

The channel itself is identical to the ambient channel, but diffuse lighting nodes (diffuse, clay, skin etc.) connected to the translucency channel act as if the normals of the surface are reversed, so that lights behind the surface cause it to be illuminated. 

A few things to note:

i) The diffuse nodes need to be exclusively attached to the translucency channel. If they are part of a tree that attaches to any other channel (e.g. Ambient) the effect is nullified. 

I presume that the direction of the diffuse normals for the specific node are determined at some time before the sampling for the entire Poser surface is carried out and the reversed state of the normals is marked as a flag on the node data object.

ii) In P6 and P7 (?) (but not P5) the "normals forward" checkbox of the diffuse node must be checked (it also works with other diffuse type nodes if they have this checkbox).

iii) When using shadows the shadow bias must be great enough for backlights to penetrate a solid object far enough to illuminate the front (camera facing) surface. i.e. if an object is too thick the front of an object won't get illuminated. It's easy enough to demonstrate the effects of the translucency channel with shadows disabled, but tweaking it to get good effects in practise (e.g. backlit ears) can be a lot harder.