There is a bug report for this @ https://www.drupal.org/node/2172871
A temporary fix available @ https://www.drupal.org/node/2172871#comment-10247397
No need to hack the core. Just add the below function in your theme or module.
/**
* Implements hook_url_outbound_alter().
*
* Fix statistics path when i18n path prefix enabled
* see: https://www.drupal.org/node/2172871
*/
function YOUR_THEME_OR MODULE_url_outbound_alter(&$path, &$options, $original_path) {
if ($original_path === 'modules/statistics/statistics.php' && isset($options['prefix'])) {
$options['prefix'] = '';
}
}