Thanks a lot for the tests and comments,
Fortunately, following your previous comment [1], I was able to find the
source of the problem and fix it [2].
The problem was a partial installation of TeX by my operating system's
package manager. It had precedence over my TeX Live installation and
created those errors. After giving precedence to my TeX Live
installation (in `PATH'), the problem was fixed.
Thanks again,
Mohammad
[1] http://lists.gnu.org/archive/html/bug-texinfo/2018-09/msg00010.html
[2] http://lists.gnu.org/archive/html/bug-texinfo/2018-09/msg00011.html
