You should use setlocale()
:
setlocale(LC_TIME, 'fr_FR');
$month_name = date('F', mktime(0, 0, 0, $i));
In this case it would set it to French. For your case it should be one of the following:
sr_BA
– Serbian (Montenegro)sr_CS
– Serbian (Serbia)sr_ME
– Serbian (Serbia and Montenegro)