The function getSupportedLanguages() is defined in file 'include.session.inc' which is referenced from 'include.general.inc' with the following code at line 3363:
if (isset($_SERVER['SERVER_PROTOCOL'])) {
$protocol = 'HTTP://';
require_once 'include.jump.inc';
require_once 'include.session.inc';
} else {
// this is being run in batch/cli mode, not from a web server
$protocol = '';
} // if
As you can see the only way for this file not to be included is if $_SERVER['SERVER_PROTOCOL'] is not being set by your web server. Can you check this out by running phpinfo(), or by stepping through with your debugger?