miltos
It's defined in the error page of template, you can see it in the file: root/templates/ja_blockk/error.php
And you can override these language constants:
TPL_ERROR_CODE = "Oops!"
TPL_FOLLOWING_PAGES = "We are sorry. But the page you are looking for cannot be found. Don’t panic, just click the big button to return home!"
TPL_LAYOUT_HOME_PAGE = "Back to Homepage"
https://docs.joomla.org/Help4.x:Languages:_Overrides
