Website only loads if the "/?lang=sl" is included into the URL?

When I try to open my website with the domain (apkzity.com) it loads ok in incognito mode but it is buggy in normal mode (the picture are not loaded, etc). But If I search for "apkzity.com/lang=en" it works.

I do not know if there is something wrong with the database or with the wordpress installation?

I host my website on OVH Cloud, have a 1-click CMS installed (wordpress), my database is edited using myPHPadmin.

If there is anybody that had the same problem, please let me know how to fix this issue.

I tried making a domain redirection but it would interfere with existing redirections that were made after I purchused my domain.

Then I tried to find the root installation folder in my database but couldn't find it (maybe I was searching in the wrong place - using myPHPadmin controll panel).