$ composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them
.
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for symfony/icu v1.2.0 -> satisfiable by symfony/icu[v1.2.0].
    - symfony/icu v1.2.0 requires lib-icu >=4.4 -> the requested linked library icu has the wrong version installed or is missing from your system, ma
ke sure to have the extension providing it.
  Problem 2
    - symfony/icu v1.2.0 requires lib-icu >=4.4 -> the requested linked library icu has the wrong version installed or is missing from your system, ma
ke sure to have the extension providing it.
    - symfony/symfony v2.3.6 requires symfony/icu ~1.0 -> satisfiable by symfony/icu[v1.2.0].
    - Installation request for symfony/symfony v2.3.6 -> satisfiable by symfony/symfony[v2.3.6].

php.ini

extension=intl.so       ; *nix
extension=php_intl.dll  ; windows

[intl]
intl.default_locale = en_utf8
intl.error_level = E_WARNING