Setting up the child theme so as to enable right-to-left WordPress?

You also need to include the RTL.css file which is in the theme too:

add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
function my_theme_enqueue_styles() {
 wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );
  wp_enqueue_style( 'rtl-style', get_template_directory_uri() . '/rtl.css' );
}

To use the rtl.css from your theme directory change the code to:

add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
function my_theme_enqueue_styles() {
 wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );
 wp_enqueue_style( 'rtl-style', get_stylesheet_directory_uri() . '/rtl.css' );
}

Make sure you copy everything from the original rtl.css file to your own.