sudo apt-get install php5-xsl
sudo /etc/init.d/apache restart
worked for me on Linux Mint 17.3 to intall XSL.
PHP 5 includes the XSL extension by default and can be enabled by adding the argument --with-xsl[=DIR] to your configure line (DIR being the libxslt installation directory).
sudo apt-get install php5-xsl
sudo /etc/init.d/apache restart
worked for me on Linux Mint 17.3 to intall XSL.
On some linux systems you might be able to simply do this:
sudo apt-get install php5-xsl
or similar.