#4: the_weekday_date

the_weekday_date.php

<?php
/**
 * Convert a post's published day to pirate when the day is Saturday.
 *
 * We won't check the string, but rather the numerical representation
 * of Saturday, just in case the days of the week are translated.
 * 
 * @see the_weekday_date(), #24781
 * 
 * @param string $day The day of the week the post was published.
 * @param string $before Output before the date.
 * @param $after Output after the date.
 *
 * @return string The day of the week.
 */
function wpdocs_piratized_saturday( $day, $before, $after ) {
  // 6 is the numerical representation of Saturday, see WP_Locale::get_weekday()
	if ( '6' == mysql2date( 'w', get_post()->post_date ) )
		return 'SatARRRday';
	return $day;
}
add_filter( 'the_weekday_date', 'wpdocs_piratized_saturday', 10, 3 );

http://fotd.werdswords.com/the_weekday_date/