Access forbidden 403 to homepage but the rest of website working Drupal 7
For reasons of module SiteMap, I needed to have folders called en, es, fr, which coincides with the suffixes of the language switcher. This was causing some problem in XAMPP while not causing any problem in Linux version. I have renamed the folders and everything is ok now.

I suspect that having an URL as example.com/fr/ which renders the homepage in french is not a good idea if you have a directory, that, if Drupal were switched off, would point to a folder example.com/fr.