When loading Kartris in a browser, an error is displayed indicating that a particular resource object is not found. On back end pages, this will typically be:
The resource object with key 'PageTitle_WelcomeToKartris' was not found.
On front end pages:
The resource object with key 'AdminBar_ViewBackend' was not found.
This is a database issue, it happens because the site cannot read/load the language strings for the page, which is the first part of the code to fail. You need to review your database and database user permissions to ensure the web site user has appropriate rights to read (and modify) the database.