Thank you musicmaster, I made what you said and it helped me to search for the problem.
I've been on this days and nights and I've just found the cause: it comes from a file added by my theme owner in order to speed up my site. The file is added to ApPageBuilder module (module used to configure the whole design and theme of my site) : /modules/appagebuilder/libs/LeoOptimization.php
I didn't know this file was added, I just deleted it until I contact him to correct it. Now the site displays well (but is slow since the file was used to speed up the site).
I would be grateful if you could check if it displays well for you now.
Now I still have the issue of faceted search and special characters...