1. Install ICU from source

wget http://download.icu-project.org/files/icu4c/56.1/icu4c-56_1-src.tgz
tar -xzvf icu4c-56_1-src.tgz
cd icu/source
./configure --prefix=/usr/local/icu
make && make install

2. Install intl for PHP

wget http://pecl.PHP.net/get/intl-3.0.0.tgz
tar -xzvf intl-3.0.0.tgz
cd intl-3.0.0
PHPize ./configure –enable-intl –with-icu-dir=/usr/local/icu
make && make install

then add the following line into PHP.ini

extension=intl.so