installation cakePHP 3

Bonjour à tous,
Lors de l'installation de cakePHP 3 via composer, j'obtiens cette erreur :

iMac-de-Olivier:~ Incolivier$ sudo composer create-project --prefer-dist cakephp/app refonte
Installing cakephp/app (3.0.3)
  - Installing cakephp/app (3.0.3)
    Loading from cache

Created project in refonte
Loading composer repositories with package information
Installing dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - cakephp/cakephp 3.0.x-dev requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.1.x-dev requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.2 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.1 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-beta3 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-beta2 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-beta1 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-alpha2 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-alpha1 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-RC2 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0-RC1 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - cakephp/cakephp 3.0.0 requires ext-intl * -> the requested PHP extension intl is missing from your system.
    - Installation request for cakephp/cakephp ~3.0 -> satisfiable by cakephp/cakephp[3.0.0, 3.0.0-RC1, 3.0.0-RC2, 3.0.0-alpha1, 3.0.0-alpha2, 3.0.0-beta1, 3.0.0-beta2, 3.0.0-beta3, 3.0.1, 3.0.2, 3.1.x-dev, 3.0.x-dev].

Résultat : Il installe installe bien un dossier contenant l'installation de cakePHP3, mais sans les dépendances. Pas très utile...
Le dossier est donc vide..
Quelqu'un a une idée ?