FIND:
return abs($diff_start_event) . ' ' . __('days left', 'cosmotheme');
and
return abs($diff_end_event) . ' ' . __('days left', 'cosmotheme');
CHANGE IN:
return 'Tra ' . abs($diff_start_event) . ' ' . __('giorni', 'cosmotheme');
and
return 'Tra ' . abs($diff_end_event) . ' ' . __('giorni', 'cosmotheme');