[WordPress] Parent/child theme l10n logic.

child-theme-functions.php

<?php 

/**
 * child-theme/functions.php
 * 
 * Loads first, before parent-theme/functions.php.
 */
function child_after_setup_theme() {

	load_child_theme_textdomain( 'child-textdomain', get_stylesheet_directory() . '/languages' );
}
add_action( 'after_setup_theme', 'child_after_setup_theme' );

// Child theme translation works, because of different textdomain.
function child_string() {
	printf( __( 'The URL of the active theme is: %s', 'child-textdomain' ), get_stylesheet_directory_uri() );
}

// Child theme translation **doesn’t** work, because parent_textdomain loads afterwards and overrides child translation.
function child_string() {
	printf( __( 'The URL of the active theme is: %s', 'parent-textdomain' ), get_stylesheet_directory_uri() );
}

parent-theme-functions.php

<?php

/**
 * parent-theme/functions.php
 * 
 * Loads after child-theme/functions.php.
 */
function parent_after_setup_theme() {

	load_theme_textdomain( 'parent-textdomain', get_template_directory() . '/languages' );
}
add_action( 'after_setup_theme', 'parent_after_setup_theme' );

// Overrides translation for identical string in child_string()
function parent_string() {
	printf( __( 'The URL of the active theme is: %s', 'parent-textdomain' ), get_template_directory_uri() );
}