This is different from some other Lisp systems, where only the base language runtime contains some C and/or assembler, and the actual application is mostly written in Lisp using an FFI (foreign function interface) for library calls. For example the GUI of Clozure CL is written in Lisp using an Objective C bridge, and not directly in Objective C and then called from Lisp.
Thus Emacs Lisp is also somewhere in a continuum of implementation and extension language - using C not only for the Emacs Lisp language runtime, but also for basic application implementation...
https://github.com/emacs-mirror/emacs/tree/master/src
Quite a bit of the actual GNU Emacs application is using libraries written in C. See for example the font code.
https://github.com/emacs-mirror/emacs/blob/master/src/font.c
This is different from some other Lisp systems, where only the base language runtime contains some C and/or assembler, and the actual application is mostly written in Lisp using an FFI (foreign function interface) for library calls. For example the GUI of Clozure CL is written in Lisp using an Objective C bridge, and not directly in Objective C and then called from Lisp.
Thus Emacs Lisp is also somewhere in a continuum of implementation and extension language - using C not only for the Emacs Lisp language runtime, but also for basic application implementation...