For my blogpost http://websupporter.net/blog/de/starter-content-fuer-themes/

starter-content-add-posts.php

<?php

add_action( 'after_setup_theme', 'theme_start_content' );
function theme_starter_content() {

	add_theme_support( 'starter-content', array(
		'posts' => array(
			'test' => array(
				'post_type' => 'page',
				'post_title' => _x( 'Das ist ein Test', 'theme-slug' ),
				'post_content' => _x( 'Hier habe ich eine Testseite angelegt.', 'theme-slug' ),
			),
		),
	) );
}