None of the files are missing (here is the Italian flag on your server, for example).
But there is something odd about your installation.
When osTicket is installed the instructions tell the user to upload the /upload folder to their server and then rename it to whatever they want. I’ve seen examples such as /helpdesk, /support, /osticket, etc.
In your case it appears that you have uploaded the contents of the /upload folder into the root directory.
It isn’t a good idea to do it this way.
Did you back up your original osTicket installation? You still need it for if/when you decide to upgrade to a newer version of osTicket (for example, v1.11.x or v.1.2.x when they are released). The original osTicket core files are useful for troubleshooting purposes.
Ideally your original osTicket files will be in a directory such as /support-old and your osTicket Awesome files in a directory such as /support.
Also, do you not use the omnik.tech domain for anything else? You don’t have a company website?
Either way I highly recommend using directories as I have described above. But if you want to keep things the way they are, here is something to try.
Open /include/ost-config.php and uncomment the ROOT_PATH directive and configure it like this:
define(‘ROOT_PATH’, ‘/‘);
Also go to Admin Panel > Settings and make sure that Helpdesk URL is simply http://omnik.tech