Drupal 7 site display unexpected symbols
Every time I have encountered this problem, it has been because I have


page level caching enabled on admin/config/development/performance
page compression enabled on admin/config/development/performance
output compression enabled in .htaccess or httpd.conf (eg, mod_deflate)


The cause is that pages are being compressed twice on the server side, but only decompressed once on the client side.  The solution is to disable page compression in Drupal.

You can add an override to your settings.php

$conf['page_compression'] = FALSE;


and alter the performance page

function MYMODULE_form_system_performance_settings_alter(&amp;$form, $form_state) {
  $form['bandwidth_optimization']['page_compression']['#default_value'] = 0;
  $form['bandwidth_optimization']['page_compression']['#disabled'] = TRUE;
  $form['bandwidth_optimization']['page_compression']['#description'] = t('Handled by Apache.');
}