E: Невозможно найти пакет php5-intl Ubuntu 16.04

Я пытаюсь обновить composer, но получаю эту ошибку:

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - The requested PHP extension ext-intl * is missing from your system. Install or enable PHP's intl extension.
  Problem 2
    - The requested package bower-asset/admin-lte could not be found in any version, there may be a typo in the package name.
  Problem 3
    - The requested package bower-asset/font-awesome could not be found in any version, there may be a typo in the package name.
  Problem 4
    - The requested package bower-asset/html5shiv could not be found in any version, there may be a typo in the package name.
  Problem 5
    - The requested package bower-asset/jquery-slimscroll could not be found in any version, there may be a typo in the package name.
  Problem 6
    - The requested package bower-asset/flot could not be found in any version, there may be a typo in the package name.

Поэтому я попытался установить расширение php5-intl, используя: sudo apt-get install php5-intl. Но, к сожалению, я получил эту ошибку ...

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package php5-intl

Итак, что мне нужно сделать, чтобы решить эту проблему? Я использую Ubuntu 16.04.