Could you change gettext-conf.php this way?:
Add this at line 19:
$set_utf8_extension='.utf8'; //Some server need this set to '.uft8' to show charset correct - else set to ''
And change line 102 to:
setlocale(LC_ALL, $language . $set_utf8_extension);
(Using an array in setlocale did not work)
***
Adding
header('Content-Type: text/html; charset=UTF-8');
to ajax.reports.php was not needed anymore.
***