Plain PDL uses C, not Fortran, routines for its calculations (except in PDL::Slatec and PDL::Minuit, which are bindings to supplied Fortran routines, if the system has a Fortran compiler). However PDL::LinearAlgebra is a binding to LAPACK. That was originally in Fortran, but increasingly parts of the implementations you'll find installed or packaged are written in C and/or C++.