As a Symfony developer you run into translations sooner or later. This is a very powerful component of the framework. But requires some additional configuration of your MAMP environment before you can start using it. I'll explain to you in short how.
First, grab the ICU libraries and build them:
$ curl -O http://download.icu-project.org/files/icu4c/220.127.116.11/icu4c-4_8_1_1-src.tgz$ tar xzvf icu4c-4_8_1_1-src.tgz$ cd icu/source$ ./runConfigureICU MacOSX$ make && sudo make install
Now you have to install the PHP INTL extension with PECL. Make sure you've added the MAMP PHP binary directory to your $PATH environment variable. Then run the following command to install the INTL extension:
$ pecl install intl
The last thing to do is add the extension=intl.so line to the php.ini file, so do that. Restart your shell and MAMP environment so they reflect the changes to the ini file.