$file = "eguide_".formatTimestamp(time(),"Ymd").".csv";
$charset = eguide_form_options('export_charset', _MD_EXPORT_CHARSET);
header("Content-Type: text/plain; Charset=".$charset);
header('Content-Disposition:attachment;filename="'.$file.'"');

and :
define('_MD_EXPORT_CHARSET', 'UTF-8');

====================================

my CVS reading tool is excel.

mbstring is :
Multibyte Support enabled
Multibyte string engine libmbfl
Multibyte (japanese) regex support enabled
Multibyte regex (oniguruma) version 4.4.4
Multibyte regex (oniguruma) backtrack check On
---------------------------
iconv is :
iconv support enabled
iconv implementation "libiconv"
iconv library version 1.11
---------------------------