Multibyte Support
Multibyte support "mbstring" is a Human Language and Character Encoding function for PHP which enables HTTP input character encoding conversion.
mbstring support is not enabled by default in PHP. If you are not sure if mbstring support is enabled, check the phpinfo page
<?php phpinfo(); ?>
if there is no section on the output of phpinfo labeled "mbstring" with the text "Multibyte Support" set to "enabled" then you do not have mbstring installed.
Use the extension_loaded class:
extension_loaded('mbstring');
You must explicitly enable the module with the "configure" option after it has been installed.
To install mbstring on Red Hat Linux-based distributions
yum install php-mbstring service httpd restart
this includes RHEL, Fedora, CentOS, Mandriva, and Intrinsic Linux. To restart Apache you can also 'httpd -k restart'.