On a vagrant box managed by a project I recently encountered this error when trying to run composer install.
Fatal error: unexpected St13runtime_error: locale::facet::_S_create_c_locale name not valid
To resolve this edit /etc/default/locale and add the following lines
Save the file then from the command line enter
Thanks to http://laravel.io/forum/08-28-2014-hhvm-instead-of-php-laravel-composer-installation-error for the information