[pjmlp]

Like most languages with modules.

Rust, Modula-2 and Ada are probably the only ones with module nesting.

[IsTom]

Notably many languages in ML family have first class modules.

[pjmlp]

Only Standard ML and OCaml, as far as I am aware.

However this is a different kind of modules, with them being present on the type system, and manipulated via functors.