I tried to search Japanese word "てすと" in search.php page, but returned "No suitable matches were found.". The Japanese word "てすと" had been already posted as both topic title and topic messege.

I tested in local host. The php.ini setting "mb_internal_encoding" is EUC-JP, not UTF-8. I'm aware that it is the cause. In fact, when I add "php_value mbstring.http_output UTF-8" into .htaccess, the problem never occurs.

I think it is better to add "php_value mbstring.http_output UTF-8" into .htaccess for this problem. Forthermore for all user who use mbstring module, I think it is better to add following sentences into .htaccess.
php_flag output_buffering Off
php_value default_charset UTF-8
php_value mbstring.language neutral
php_flag mbstring.encoding_translation On
php_value mbstring.http_input auto
php_value mbstring.http_output UTF-8
php_value mbstring.internal_encoding UTF-8
php_value mbstring.substitute_character none
php_value mbstring.func_overload 0

Especially I think "php_value mbstring.func_overload 0" is important and necessary for e-mailing.

Is'nt it impossible to have added above sentences into .htaccess file as download pacｋage? I would be happy if dev team granted my wishes.