Labels include

Hi.

I would like to create a labels.php file to change the labels values from my WordPress backend.

I have a labels.php that I include in my functions.php.

Now, in one of my custom post type I want to add the variable instead of the static names. e.x.

function my_custom_post_textpages() {
	$labels = array(
		'name'               => _x( 'Description Texts', 'post type general name' ),
		'singular_name'      => _x( 'Description Texts', 'post type singular name' ),
		'add_new'            => _x( 'Add New', '' ),
		'add_new_item'       => __( 'Add New Description Text' ),
		'edit_item'          => __( 'Edit Description Text' ),
		'new_item'           => __( 'New Description Text' ),
		'all_items'          => __( 'All Description Texts' ),
		'view_item'          => __( 'View Description Texts' ),
		'search_items'       => __( 'Search Description Texts' ),
		'not_found_in_trash' => __( 'No Description Texts found in the Trash' ),
		'not_found'          => __( 'No Description Texts found' ),
		'parent_item_colon'  => '',
		'menu_name'          => 'Description Texts'

In order to change the menu_name I put in my labels.php define($backendMenu,"Title 1"); so I would put $backendMenu instead of ‘Description Texts’, but nothing happens. How can I load the $backendMenu value?

Thanks