Multilingual site with sub folders

Site URL: https://isere-ski-rando.com

Hi,

I have a website built in french and I want to add english support. Following available tutorials

for me do not work as I use folders. I.e at the root of the website I have few pages and two folders.

These folders are used to organised the navigation : Something like the following. 

/accueil

/actualités

activitiés/activité1

activitiés/activité2

The tutorial I am trying to follow also use folders so my site should become

/cover-page

/fr/accueil

/fr/actualités

/fr/activitiés/activité1

/fr/activitiés/activité2

/eng/home

/eng/news

/eng/activities/activity1

/eng/activities/activity2

The issue I am facing is that I cannot add a sub-folder to a folder.  The ui only let me add pages 

Any help on this will be welcome.

regards 

E Jannetti