No insert slideshow button in gallery

I’ve been trying for many hours now to insert a slideshow into one of my pages. Read tutorials, tried to add the shortcode [slideshow] to the HTML window, read all I could in forums, but nothing seems to work. Here is a link to one page I am trying to add a slideshow to . http://desjardinsgreenconcepts.com/fr/produits/bioecrans-sur-roues/ I know there are plugins out there that I could use, but I want the same slideshow that is already on the English version: http://desjardinsgreenconcepts.com/wp/our-products/bio-screen-on-wheels/. Also tried clearing the cache etc… There is no insert slideshow button in the gallery. I also removed the elegant theme and reinstalled it…. Can somebody help me solve the problem?