Filter WordPress admin bar text

gistfile1.php

/**
 * Filter admin bar strings.
 */
function md_filter_admin_bar_strings( $translation, $original_text, $domain ) {
	if ( 'About WordPress' == $original_text )
		$translation = 'About this site';

	return $translation;
}

/**
 * Register gettext filter for admin bar.
 */
function md_add_ab_gettext_filter() {
	add_filter( 'gettext', 'md_filter_admin_bar_strings', 10, 3 );
}
add_action( 'admin_bar_init', 'md_add_ab_gettext_filter', 1 );
add_action( 'wp_before_admin_bar_render', 'md_add_ab_gettext_filter', 1 );

/**
 * Unregister gettext filter admin bar.
 */
function md_remove_ab_gettext_filter() {
	remove_filter( 'gettext', 'md_filter_admin_bar_strings', 10, 3 );
}
add_action( 'wp_after_admin_bar_render', 'md_remove_ab_gettext_filter', 1000 );