Simple PHP i18n (internationalization) (Haven't tested it, written on the fly)

en.php

<?php

$lang = array(
  'createaccount' => 'Create Account',
  'welcome' => 'Welcome %s!',
  // ...
);

simplei18n.php

<?php
// You'd put these in your class constructor (remember to change to $this->lang)

// Loads the language file based on user agent
$lang = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2);

// Load it or default to English
if (file_exists('lang/'.$lang.'.php')) {
  include('lang/'.$lang.'.php');
}else{
  include('lang/en.php');
}


// Now the function/method
function __($string, $custom = array()) {
  if ($lang[$string]) {
    $return = $lang[$string];
    $i = 0;
    while (strpos($return, '%s')) {
      $return = str_replace('%s', $custom[$i], $return, $temp=1);
      $i++;
    }
    return $return;
  }else{
    return 'Unrecognized language string!'; // or false if you want to catch it
  }
}


// Usage
echo __('createaccount');
echo __('welcome', array('John'));