Thomas Bucaioni wrote:

> When pressing the TAB key, the indentation doesn't happen. Even, the
> text is translated as in a Word or LibreOffice document.

Please give a minimal complete example starting from emacs -Q.

> In GNU Emacs 24.5.1 (i686-pc-linux-gnu, GTK+ Version 3.22.11)

Please try the current release (26.1 at time of writing).