To split an string like this: "日、に、本、ほん、語、ご" using the "、" delimiter i used:

     $v = mb_split('、',"日、に、本、ほん、語、ご");

but didn't work.

The solution was to set this before:

       mb_regex_encoding('UTF-8');
      mb_internal_encoding("UTF-8"); 
     $v = mb_split('、',"日、に、本、ほん、語、ご");

and now it's working:

Array
(
    [0] => 日
    [1] => に
    [2] => 本
    [3] => ほん
    [4] => 語
    [5] => ご
)