Internationalize / translate custom post types & taxonomies

Question

I've created custom post type and taxonomy via generator, but not quite sure how to make it translatable. Google doesn't help in this. I have no idea where to put text-domain here and things what I've tried made taxonomies don't work at all.

Thanks in advance.

The code:

    add_action( 'init', 'register_cpt_portfolio' );
    function register_cpt_portfolio() {

        $labels = array( 
            'name' => _x( 'Portfolios',  'portfolio'),
            'singular_name' => _x( 'single-portfolio',  'portfolio' ),
            'add_new' => _x( 'Add New', 'portfolio' ),
            'add_new_item' => _x( 'Add New Portfolio', 'portfolio' ),
            'edit_item' => _x( 'Edit Portfolio',  'portfolio' ),
            'new_item' => _x( 'New Portfolio', 'portfolio' ),
            'view_item' => _x( 'View Portfolio',  'portfolio' ),
            'search_items' => _x( 'Search Portfolios',  'portfolio' ),
            'not_found' => __( 'No portfolios found',  'portfolio' ),
            'not_found_in_trash' => _x( 'No portfolios found in Trash',  'portfolio' ),
            'parent_item_colon' => _x( 'Parent Portfolio:', 'portfolio' ),
            'menu_name' => _x( 'Portfolio',  'portfolio' ),
        );

        $args = array( 
            'labels' => $labels,
            'hierarchical' => false,
            'supports' => array( 'title', 'editor', 'thumbnail' ),
            'taxonomies' => array( 'portfolio_taxonomy' ),
            'public' => true,
            'show_ui' => true,
            'show_in_menu' => true,
            'show_in_nav_menus' => true,
            'publicly_queryable' => true,
            'exclude_from_search' => false,
            'has_archive' => true,
            'query_var' => true,
            'can_export' => true,
            'rewrite' => true,
            'capability_type' => 'post'
        );

        register_post_type( 'portfolio', $args );
    }    


    add_action( 'init', 'register_taxonomy_portfolio_taxonomy' );

    function register_taxonomy_portfolio_taxonomy() {

        $labels = array( 
            'name' => _x( 'Portfolio Categories',  'portfolio_taxonomy' ),
            'singular_name' => _x( 'Portfolio Category', 'portfolio_taxonomy' ),
            'search_items' => _x('Search Portfolio Categories',  'portfolio_taxonomy'),
            'popular_items' => _x( 'Popular Portfolio Categories',  'portfolio_taxonomy' ),
            'all_items' => _x('All Portfolio Categories', 'portfolio_taxonomy' ),
            'parent_item' => _x('Parent Portfolio Category',  'portfolio_taxonomy' ),
            'parent_item_colon' => _x( 'Parent Portfolio Category:',  'portfolio_taxonomy' ),
            'edit_item' => _x( 'Edit Portfolio Category', 'portfolio_taxonomy' ),
            'update_item' => _x( 'Update Portfolio Category', 'portfolio_taxonomy' ),
            'add_new_item' => _x( 'Add New Portfolio Category', 'portfolio_taxonomy'),
            'new_item_name' => _x( 'New Portfolio Category',  'portfolio_taxonomy' ),
            'separate_items_with_commas' => _x( 'Separate portfolio categories with commas', 'portfolio_taxonomy'),
            'add_or_remove_items' => _x( 'Add or remove portfolio categories',  'portfolio_taxonomy' ),
            'choose_from_most_used' => _x( 'Choose from the most used portfolio categories', 'portfolio_taxonomy' ),
            'menu_name' => _x( 'Portfolio Categories','portfolio_taxonomy'),
        );

        $args = array( 
            'labels' => $labels,
            'public' => true,
            'show_in_nav_menus' => true,
            'show_ui' => true,
            'show_tagcloud' => true,
            'hierarchical' => true,
            'rewrite' => true,
            'query_var' => true
        );

        register_taxonomy( 'portfolio_taxonomy', array('portfolio'), $args );
    }

Answer 1

Since you have already figured out what the text domain is - the last parameter of __() - I want to add something most people forget when custom post types or taxonomies are made translatable: slugs.

Your post type or taxonomy name can mean something very different or even embarrassing in another language. Or it can contain letters that are not available (like the famous i in Turkish) and therefore hard to type.

See untranslatable slugs as bugs in your code.

The rewrite argument for register_taxonomy() and register_post_type() accepts an array. One of the array keys is slug. Use it, make it translatable too:

register_post_type( 
    'post_type_name', 
    array (
        'rewrite' => array (
            'slug' => _x( 'post_type_name', 'URL slug', 'your_text_domain' )
        )
    )
);
register_taxonomy( 
    'taxonomy_name',
    array ( 'post', 'post_type_name' ), 
    array (
        'rewrite' => array (
            'slug' => _x( 'taxonomy_name', 'URL slug', 'your_text_domain' )
        )
    )
);

The function _x() uses a context parameter. This will help translators to see where the string will be used.