wpml-the-content-filter.php

<?php
function wpml_the_content_filter( $content ) {

	global $post, $sitepress;

	$element_type         = 'post_' . $post->post_type;
	$trid                 = $sitepress->get_element_trid( $post->ID, 'post_' . $post->post_type );
	$element_translations = apply_filters( 'wpml_get_element_translations', null, $trid, $element_type );
	$translation_type     = apply_filters( 'wpml_element_translation_type', null, $post->ID, $post->post_type );

	if ( WPML_ELEMENT_IS_NOT_TRANSLATED !== $translation_type ) {
		$translations = '';
		$duplicates   = '';
		if ( 0 < count( $element_translations ) ) {
			foreach ( $element_translations as $language_code => $element_translation ) {
				if ( (int) $element_translation->element_id !== $post->ID ) {
					$element_translation_type = apply_filters( 'wpml_element_translation_type', null, $element_translation->element_id, $post->post_type );
					$element_language         = apply_filters( 'wpml_post_language_details', null, $element_translation->element_id );

					$translation_url = get_permalink( $element_translation->element_id );
					$translation_url = $sitepress->convert_url( $translation_url, $language_code );
					$element_link    = '<a href="' . esc_url( $translation_url ) . '">' . $element_language['display_name'] . '</a>';

					if ( WPML_ELEMENT_IS_TRANSLATED === $element_translation_type || (bool) $element_translation->original ) {
						$translations .= '<li>';
						$translations .= $element_link;
						$translations .= '</li>';
					}
					if ( WPML_ELEMENT_IS_A_DUPLICATE === $element_translation_type ) {
						$duplicates .= '<li>';
						$duplicates .= $element_link;
						$duplicates .= '</li>';
					}
				}
			}
		}

		if ( '' !== $translations ) {
			$content .= '<p>This post is also available in: </p>';
			$content .= '<ul>';
			$content .= $translations;
			$content .= '</ul>';
		}
		if ( '' !== $duplicates ) {
			$content .= '<p>This post is duplicated in: </p>';
			$content .= '<ul>';
			$content .= $duplicates;
			$content .= '</ul>';
		}
	}

	return $content;
}

add_filter( 'the_content', 'wpml_the_content_filter' );