<?php


$arr = Array( [2] => Array( [product_id] => 18 [language_id] => 2 [image] => product_en.jpg ) [1] => Array( [product_id] => 18 [language_id] => 1 [image] => product_tr.jpg ) [3] => Array( [product_id] => 18 [language_id] => 1 [image] => product_ar.jpg ) );

$arr2 = array_map(function($arr) {
return array_merge($arr, [
'category' => 'shoes'
]);
}, $arr);