mb_substr() is a multibyte-safe version of
substr(), meaning it works with characters as opposed to bytes. This is most noticeable in UTF-8, where many characters are represented by two or more bytes.
According to the installation instructions,
mbstring is not a built-in extension. You must enable it by having the appropriate files and configuring PHP correctly. Some information can be found in the link provided, your webhost should be able to help you with the rest.
Find PHP function
mb_substr() in your
Throw this into a terminal:
php -m | grep mb
mbstring shows up then it should work.
Look in your php.ini file. Search for extension= and look through the list of extensions. If there is one with the name mbstring in it then the extension should be installed. If the line is commented out (has a ; in-front of it) then it is not enabled... remove the
Restart Apache (or whatever server you are using).