[BUG] LANG=fr_FR.UTF-8 org-clock "not at timestamp"

[Ruijie Yu via "General discussions about Org-mode." <emacs-orgmode@gnu.org>]

Hello,

I am investigating test failures with LANG=fr_FR.UTF-8 amongst some
other locales.  I noticed that the test
`test-org-clok/org-clock-timestamps-change' in
testing/lisp/test-org-clock.el around line 92 failed with "not at
timestamp", which I presume reveals a genuine bug.

To simplify, here is a reproducer:

--8<---------------cut here---------------start------------->8---
(require 'org-clock)
(with-temp-buffer
  (org-mode)
  (insert "CLOCK: [2023-02-19 Sun 22:30]--[2023-02-20 Mon 00:35] =>  2:05")
  (goto-char 25)                        ; 2|2:30
  (org-clock-timestamps-change 'down 1))
--8<---------------cut here---------------end--------------->8---

The error appears: "Not at timestamp".  I think it is due to the "." in
French day-of-week words, such as "dim.", "lun.", etc.  Something must
not be expecting punctuations in that place.

Reproduced in newest orgmode, and 1-month old Emacs master.

-- 
Best,


RY

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