I am Localizing my php application. I have a dilemma on choosing best method to accomplish the same.

Method 1: Currently am storing words to be localized in an array in a php file

<?php

$values = array (
                        'welcome' => 'bienvenida'
                ); 

?>

I am using a function to extract and return each word according to requirement

Method 2: Should I use a txt file that stores string of the same?

<?php
$welcome = 'bienvenida'; 
?>

My question is which is a better method, in terms of speed and effort to develop the same and why?

Edit: I would like to know which method out of two is faster in responding and why would that be? also, any improvement on the above code would be appreciated!!