Unless you've intentionally attempted to set a non-english language during install (and that language hasn't been defined), that should never happen.

index.php says:
Code:
  require('includes/application_top.php');
application_top says:
Code:
  $language = 'english';
and returns back to index.php, which then says:
Code:
  require('includes/languages/' . $language . '.php');
Perhaps your /zc_install/includes/application_top.php file is blank and needs to be re-uploaded ?
You may have to get your host involved to find out why a defined variable is showing up blank when an otherwise-functional PHP script is run on their server.