Are schemes similar to Hurd translators?

Or is there something else with similar capabilities?

I don’t know much about Hurd translators. Schemes are filesystems that are identified by a name.

The concepts seem quite related; with the difference that Hurd translators are filename-/directory-based hooks inside the same root filesystem namespace while Redox schemes each have their own namespace.

Also related are Plan 9 filesystem namespaces, though the filesystems are mounted in place, but also represent functionality that you can place inside the filesystem.

In Plan 9, each user can have his own view of filesystem mounts = one user can see mounted filesystems, which other users do not. So visibility is/can be different in Plan 9 from Hurd translators and Redox schemes.

That’s at least how I understand these concepts.