This is an old thread, i thought i would just add my solution for my environment:
CentOS 7.5 x64 
Apache version: Apache/2.4.34
PHP version: 7.1.22 [PHP Switcher]
MySQL version: 10.1.37-MariaDB
------------------------------
Below is what i followed taken from 
https://unix.stackexchange.com/questions/345106/how-to-install-extenion-php-intl-in-centos7----------------------------
There are two ways to install php-intl in centos-os (centos ver 2017.09), php version > 7.0
Update system, and try install php-intl directly
Install php-intl through IUS and REMI repositories
1. Update system, and try install php-intl directly
UPDATE SYSTEM command
sudo yum update
INSTALL php70-intl extension
sudo yum install -y php70-intl
2. Install php-intl through IUS and REMI repositories
INSTALL IUS repository (
http://iuscommunity.org/pages/Repos.html#release-packages)
cd /opt/
sudo wget 
https://rhel7.iuscommunity.org/ius-release.rpmsudo rpm -Uvh ius-release*.rpm 
If getting epel error like epel-release = 7 is needed by ius-release-1.0-15.ius.el7.noarch you need to install epel-7 through following command, and retry above command
sudo rpm -Uvh 
https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpmUpdate system via
sudo yum update 
Retry ius install
sudo rpm -Uvh ius-release*.rpm 
After IUS is successfully installed, run update system again through command sudo yum update 
INSTALL php-intl THROUGH REMI REPOSITORY
Enable remi (temporarily) and install php-intl
sudo yum --enablerepo=remi install php-intl
IF getting ERROR like "Error getting repository data for remi, repository not found", you need to install remi repository first, then run above command
yum install 
http://rpms.remirepo.net/enterprise/remi-release-7.rpmIF getting ERROR like "php70-common-7.0.32-1.31.amzn1.x86_64 conflicts php-common < 5.5.22-1.98" then you need to install php70-intl directly in place of remi repository
sudo yum install -y php70-intl
------------------------------- Above is the instuction from the reference URL ---------------
Also i had a conflict of php_intl version ( 5.4.16-45.el7), 
Error showed: "Package php-intl-5.4.16-45.el7.x86_64 already installed and latest version".
so i removed the old version first:
[root@cp ~]# yum remove php-intl
And removed the dependencies:
[root@cp ~]# yum remove  php-common-5.4.16-45.el7.x86_64
Than, list the available package:
[root@cp ~]# yum list php*intl
Installed Packages
php-intl.x86_64                     5.4.16-45.el7                      @base  (This was removed by me earlier)
Available Packages
php54-php-intl.x86_64               5.4.45-15.el7.remi                 remi-safe
php55-php-intl.x86_64               5.5.38-9.el7.remi                  remi-safe
php56-php-intl.x86_64               5.6.38-2.el7.remi                  remi-safe
php56u-intl.x86_64                  5.6.38-1.ius.el7                   ius
php70-php-intl.x86_64               7.0.32-1.el7.remi                  remi-safe
php70u-intl.x86_64                  7.0.32-1.ius.el7                   ius
php71-php-intl.x86_64               7.1.24-1.el7.remi                  remi-safe  (**I need this version)
php71u-intl.x86_64                  7.1.23-1.ius.el7                   ius
php72-php-intl.x86_64               7.2.12-1.el7.remi                  remi-safe
php72u-intl.x86_64                  7.2.11-1.ius.el7                   ius
php73-php-intl.x86_64               7.3.0~rc5-1.el7.remi               remi-safe
// install new php_intl version with its dependencies:
[root@cp ~]# yum install -y php71u-intl.x86_64
-------------
Success Log
-------------
[root@cp ~]# yum install -y php71u-intl.x86_64
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.0x.sg
 * extras: mirror.0x.sg
 * ius: hkg.mirror.rackspace.com
 * remi-safe: mirrors.thzhost.com
 * updates: mirror.0x.sg
Resolving Dependencies
--> Running transaction check
---> Package php71u-intl.x86_64 0:7.1.23-1.ius.el7 will be installed
--> Processing Dependency: php-common(x86-64) = 7.1.23-1.ius.el7 for package: ph                                                                                                             p71u-intl-7.1.23-1.ius.el7.x86_64
--> Running transaction check
---> Package php71u-common.x86_64 0:7.1.23-1.ius.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
 Package              Arch          Version                    Repository  Size
================================================================================
Installing:
 php71u-intl          x86_64        7.1.23-1.ius.el7           ius        222 k
Installing for dependencies:
 php71u-common        x86_64        7.1.23-1.ius.el7           ius        1.1 M
Transaction Summary
================================================================================
Install  1 Package (+1 Dependent package)
Total download size: 1.3 M
Installed size: 9.1 M
Downloading packages:
warning: /var/cache/yum/x86_64/7/ius/packages/php71u-common-7.1.23-1.ius.el7.x86                                                                                                             _64.rpm: Header V4 DSA/SHA1 Signature, key ID 9cd4953f: NOKEY
Public key for php71u-common-7.1.23-1.ius.el7.x86_64.rpm is not installed
(1/2): php71u-common-7.1.23-1.ius.el7.x86_64.rpm           | 1.1 MB   00:01
(2/2): php71u-intl-7.1.23-1.ius.el7.x86_64.rpm             | 222 kB   00:01
--------------------------------------------------------------------------------
Total                                              1.0 MB/s | 1.3 MB  00:01
Retrieving key from file:///etc/pki/rpm-gpg/IUS-COMMUNITY-GPG-KEY
Importing GPG key 0x9CD4953F:
 Userid     : "IUS Community Project <coredev@iuscommunity.org>"
 Fingerprint: 8b84 6e3a b3fe 6462 74e8 670f da22 1cdf 9cd4 953f
 Package    : ius-release-1.0-15.ius.el7.noarch (installed)
 From       : /etc/pki/rpm-gpg/IUS-COMMUNITY-GPG-KEY
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : php71u-common-7.1.23-1.ius.el7.x86_64                        1/2
  Installing : php71u-intl-7.1.23-1.ius.el7.x86_64                          2/2
  Verifying  : php71u-common-7.1.23-1.ius.el7.x86_64                        1/2
  Verifying  : php71u-intl-7.1.23-1.ius.el7.x86_64                          2/2
Installed:
  php71u-intl.x86_64 0:7.1.23-1.ius.el7
Dependency Installed:
  php71u-common.x86_64 0:7.1.23-1.ius.el7
Complete!
---
If you spotted error in the output, it may be conflict with older or your existing php_intl installed package version.
Below is my log and what to look out for:
Error in the output i spotted that made me removed the conflict package
---
[root@cp ~]# yum install -y php71u-intl.x86_64
Resolving Dependencies
--> Running transaction check
---> Package php71u-intl.x86_64 0:7.1.23-1.ius.el7 will be installed
--> Processing Dependency: php-common(x86-64) = 7.1.23-1.ius.el7 for package: ph                                                                                                             p71u-intl-7.1.23-1.ius.el7.x86_64
--> Running transaction check
---> Package php71u-common.x86_64 0:7.1.23-1.ius.el7 will be installed
--> Processing Conflict: php71u-common-7.1.23-1.ius.el7.x86_64 conflicts php-com                                                                                                             mon < 7.1.23-1.ius.el7
--> Finished Dependency Resolution
Error: php71u-common conflicts with php-common-5.4.16-45.el7.x86_64
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest
*** Above showed conflict package to remove
[root@cp ~]# yum remove  php-common-5.4.16-45.el7.x86_64
--------------------------------------------------------------------------
After I installed the intl package, i logged in to CWP and use the PHP Version Switcher and ticked intl extension
and click save and build button.
After some time (30 minutes), i check that the building is completed from the alert message and log.
I restarted the apache, and clicked php info and the intl was shown on the page (before that it was not there).
The installation script that checked for intl also no longer prompted error for INTL not found.