The optional module, intl, is not installed, or has been disabled

According to the PHP manual this module provides Internationalization Functions. If your site is multi-lingual then this will be important to you.

If you are using a web host who maintains PHP installation for you, then you will need to contact them to install the module.

If you manage your own web host then you can follow an install guide like this one: https://www.iteron.co.za/?page_id=17204

For Linux-based Server (assuming you have root access)

Make sure the php_intl.so file exists within your php extensions directory, find the extensions directory by:
    using phpinfo()
    running this command: php -r "echo ini_get('extension_dir');"
    (note: both options gets the extension_dir right from the PHP runtime configuration)

If the file exists:
    search for the config file (php.ini, usually /etc/php.ini) and open it
    Make sure the line “extension=php_intl.so” is existing and not commented
    Restart the web server (usually sudo service httpd restart)
    Check if the extension is enabled using phpinfo()
If the file doesn’t exist
    Check your php version by running the “php -v” command
    For PHP 5 install the php-intl package using your package manager – package managers and commands
        Most common: apt-get install php-intl (for ubuntu-based linux) or yum install php-intl (for CentOS)
    For PHP 7, install the php7.x-intl (depending on your php version)
    Repeat the steps for the case in which the file exists

For Windows-based Server

Make sure the php_intl.dll file exists within your php extensions directory
    for separately installed PHP: C:\path\to\php\ext\
    for xampp: C:\path\to\xampp\php\ext
    (note: your drive letter might be different)
If the file exists:
    search for the config file (php.ini, usually in the same folder as the php executable) and open it
    Make sure the line “extension=php_intl.dll” is existing and not commented
    Restart the web server (usually apache)
    Check if the extension is enabled using phpinfo()
If the file doesn’t exist:
    Check your php version by running the “php -v” command
    Download the PHP version that corresponds to yours from the PHP Downloads Page (TS/NTS, x86/x64)
        To find thread safety for php, run: php -i | findstr “Thread” , source & more info.
    Search for the php_intl.dll file in the ext folder in that version and copy it in your php\ext folder
    Repeat the steps for the case in which the file exists