Introduction to Hurd translators
debian.org
debian.org
And how about the context switch cost? being used to Linux, I'd think that the execution flow has to jump back and forth between kernel and user space to call the translators, and again and again if you chain them?
(Edit: Emphasis on the "I think"!)
HURD is a micro-kernel so almost everything that traditionally lives in the kernel on Linux systems would be implemented as a translator in a HURD system (apart from very low-level virtual memory and CPU management).