Detect all languages used in org-babel src blocks in a file.

detect-org-babel-languages.el

(defun org-babel-get-all-src-block-info ()
  "Get information on all src blocks in an org file."
  (interactive)
  (let ((lst '()))
    (save-excursion
      ;; Go to the beginning of buffer
      (beginning-of-buffer)
      (while (condition-case err
                 ;; Try to move to the next src block.
                 (org-next-block nil nil org-babel-src-block-regexp)
               ;; If user-error is encountered, nil.
               ;; Otherwise, the evaluation result returns.
               (user-error nil))
        ;; Add information to the list.
        (add-to-list 'lst (org-babel-get-src-block-info)))
      ;; Return list
      lst)))

(defun org-babel-extract-lang-from-src-block-info (info)
  "Extract language name from src block information.

This is just the car of src block information.
Created to be clear about the intention of the code."
  (car info))

(defun org-babel-get-all-src-langs ()
  "Get all languages used src blocks."
  (interactive)
  (mapcar #'org-babel-extract-lang-from-src-block-info
          (org-babel-get-all-src-block-info)))