In the development branch, Sodium uses the same chunk rendering shader for both the opaque and translucent render pass. The opaque pass currently drops fragments which are less than 50% transparent in order to create a "cutout" appearance, which leads to translucent textures not rendering correctly at all.

The issue is fairly simple, but I'm still hashing out how we want to structure this in the codebase.

This was solved in Sodium 0.5.