Copy and synchronize WordPress posts programmatically with Polylang

sync_posts.php

<?php

$pll = new PLL_Admin( PLL()->links_model );
$pll->add_filters();
$pll_pro = new Polylang_Pro();
$pll_pro->load_modules( $pll );

global $wpdb;

$post_type = 'your-post-type';
$total     = intval( $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->posts WHERE post_type = %d", $post_type ) ) );
$per_loop  = 50;
$max_pages = ceil( $total / $per_loop );

for ( $page = 1; $page <= $max_pages; $page ++ ) {
	$the_query = new \WP_Query( [
		'post_type'      => $post_type,
		'posts_per_page' => $per_loop,
		'no_found_rows'  => true,
		'paged'          => $page,
		'lang'           => 'your-primary-language',
	] );

	if ( $the_query->have_posts() ) {
		foreach ( $the_query->get_posts() as $item ) {
			// Loop all languages which to post should be synced to.
			foreach ( [ 'sv', 'en' ] as $lang ) {
				$pll->sync_post->copy_post( $item->ID, $lang, true );
			}
		}
	}
}