(require 'parse-time)

(defun parse-time-fr (f &rest args)
  "Call the function F with arguments ARGS with `parse-time-months' and
`parse-time-weekdays' set to unaccented French."
  (let ((parse-time-months '(("jan" . 1)
			     ("fev" . 2)
			     ("mar" . 3)
			     ("avr" . 4)
			     ("mai" . 5)
			     ("jun" . 6)
			     ("jul" . 7)
			     ("aou" . 8)
			     ("sep" . 9)
			     ("oct" . 10)
			     ("nov" . 11)
			     ("dec" . 12)
			     ("janvier" . 1)
			     ("fevrier" . 2)
			     ("mars" . 3)
			     ("avril" . 4)
			     ("mai" . 5)
			     ("juin" . 6)
			     ("juillet" . 7)
			     ("aout" . 8)
			     ("septembre" . 9)
			     ("octobre" . 10)
			     ("novembre" . 11)
			     ("decembre" . 12)))
	(parse-time-weekdays '(("dim" . 0)
			       ("lun" . 1)
			       ("mar" . 2)
			       ("mer" . 3)
			       ("jeu" . 4)
			       ("ven" . 5)
			       ("sam" . 6)
			       ("dimanche" . 0)
			       ("lundi" . 1)
			       ("mardi" . 2)
			       ("mercredi" . 3)
			       ("jeudi" . 4)
			       ("vendredi" . 5)
			       ("samedi" . 6))))
    (apply f args)))

(advice-add 'org-read-date :around #'parse-time-fr)