Close #13130 (LaTeX docs about index creation) (#13139)

Author: jfbu

CHANGES.rst

@@ -23,6 +23,9 @@ Bugs fixed
 
 * #13060: HTML Search: use ``Map`` to store per-file term scores.
   Patch by James Addison
+* #13130: LaTeX docs: ``pdflatex`` index creation may fail for index entries
+  in French.  See :confval:`latex_use_xindy`.
+  Patch by Jean-François B.
 * LaTeX: fix a ``7.4.0`` typo in a default for ``\sphinxboxsetup``
   (refs: PR #13152).
   Patch by Jean-François B.

doc/usage/configuration.rst

@@ -3157,6 +3157,9 @@ These options influence LaTeX output.
    * The default is :code-py:`False` for :code-py:`'pdflatex'`,
      but :code-py:`True` is recommended for non-English documents as soon
      as some indexed terms use non-ASCII characters from the language script.
+     Attempting to index a term whose first character is non-ASCII
+     will break the build, if :confval:`latex_use_xindy` is left to its
+     default :code-py:`False`.
 
    Sphinx adds some dedicated support to the :program:`xindy` base distribution
    for using :code-py:`'pdflatex'` engine with Cyrillic scripts.