It doesn't make sense that a language that compiles to C can't support nested functions, just because C doesn't.
All the transpiler has to do is invent a globally unique name for each function, for instance. Of course they might not have implemented it yet, but there shouldn't be any firm reason why it can't be done.
Procedures can appear at the top level in a module as well as inside other scopes, in which case they are called nested procs. A nested proc can access local variables from its enclosing scope and if it does so it becomes a closure.
All the transpiler has to do is invent a globally unique name for each function, for instance. Of course they might not have implemented it yet, but there shouldn't be any firm reason why it can't be done.