Internationalization PHP 1

index.php

<?php

class Person
{
    const VERSION = '1.0.0';

    public $firstName;
    public $lastName;
    public $dob;


    function __construct($firstName, $lastName, $dob)
    {
        $this->firstName = $firstName;
        $this->lastName = $lastName;
        $this->dob = $dob;
    }

    public function printInfo()
    {
        $age = $this->calculateAge();
        echo sprintf(_("Hello my name is %s %s and I'm %s\n"), $this->firstName, $this->lastName, $age);
    }

    public function goodBye()
    {
        echo _("That's it, good bye!\n");
    }

    public function printVersion()
    {
        echo sprintf("\n(running version %s)\n", self::VERSION);
    }

    private function calculateAge()
    {
        $dob = date_create($this->dob);
        $now = date_create();
        $age = date_diff($dob, $now)->format("%y");
        $response = null;

        if($age < 18) {
            $response = sprintf(_("%s years which means I'm a teen"), $age);
        } else {
            $response = sprintf(_("%s years which means I'm a grown up"), $age);
        }

        return $response;
    }
}

$p = new Person(
    'John',
    'Wayne',
    '1980-01-20'
);
$p->printInfo();
$p->goodBye();
$p->printVersion();