ROOT
  - /locale
    - /en_US
      - phd.mo
      - phd.po
  - File1.php
  - File2.php

<?php echo _("This is a sample"); ?>

$language = "en_US";
putenv("LANG=".$language);
setlocale(LC_ALL, $language);

// Set the text domain as "phd"
$domain = "phd";
bindtextdomain($domain, "Locale");
bind_textdomain_codeset($domain, 'UTF-8');

textdomain($domain);