Mbstring stands for multi-byte string, this Mbstring-php extension can support for storing and displaying multi-byte characters in PHPKB software working with Unicode strings. The Mbstring provides multibyte-specific string functions and this can helps multi-byte encoding in PHP.

On Ubuntu:

apt-get update

apt-get install php7.2-mbstring

sudo apt-get install libapache2-mod-php7.2

or
apt-get install php-mbstring
 

On CentOS:

yum update

sudo yum install php72-php-mbstring

or
yum install php-mbstring


Once you have installed Mbstring in your instance configure the php.ini file, just add a line inside the php.ini and restart the webserver NGINX or Apache2,

For Linux,
 
extension=mbstring.so


If you are using Ubuntu operating system use the command below,

NGINX:

systemct restart nginx.service


Apache:

systemct restart apache2.service


If you are using CentOS operating system use the command below,

NGINX:

systemct restart nginx.service


Apache:

systemct restart httpd.service


Windows,

If you are using PHP on Windows add the line in php.ini and restart IIS using the command below,
 
extension = php_mbstring.dll

From the Start menu, click Run.
In the Open box, type cmd, and click OK.
At the command prompt, type

iisreset /noforce