Composer – the requested PHP extension mbstring is missing from your system [closed]

sudo apt-get install php-mbstring

# if your are using php 7.1
sudo apt-get install php7.1-mbstring

# if your are using php 7.2
sudo apt-get install php7.2-mbstring

# if your are using php 7.4
sudo apt-get install php7.4-mbstring