Translate post-type-archive-slug when different from post-type-slug. WPML allows translating custom post-type slug, but not the custom post-type-archive slug

translate-custom-post-type-archive-slug.php

<?php

/**
 * Translate post-type-archive-slug when different from post-type-slug.
 *
 * You can have your archive slug set to, for example /books and the singles on /book/title by setting
 * $args['rewrite'] => [ 'slug' => 'book', ... ];
 * $args['has_archive'] => 'books';
 * when registering your post_type
 *
 * WPML supports translating the single-slug, but not the archive-slug.
 *
 * Following code allows that. It's a 3-part solution, all 3 parts are needed.
 *
 * After implementation:
 *
 * 1. save permalinks (will register the strings with WPML)
 * 2. use WPML string translation to translate the strings, found in text-domain "post-type-archive-slug"
 * You may need to set the correct source-language for the text-domain using the WPML String Translation tools.
 * 3. save permalinks (will update rewrite rules for tanslations)
 *
 * If you don't want to use WPML String Translation, change the text-domain post-type-archive-slug to that of your theme
 * or plugin and register the strings by putting a line like this:
 * $not_used = __('archive-slug', 'text-domain');
 * in your theme or plugin and scan the files with your favorite POMO-editor.
 *
 * Make sure that all this is done in WP backend when on the default (primary) language, see [this comment](https://gist.github.com/senlin/1adf65ae297c32142e765628fce194ad?permalink_comment_id=5351512#gistcomment-5351512) 
 *
 * For more information:
 * @see https://developer.wordpress.org/apis/handbook/internationalization/localization/#translating-themes-and-plugins
 *
 * 
 * Part 1: filter the link generation. This works on the page.
 */

add_filter( 'post_type_archive_link', function ( $permalink, $post_type ) {
	$post_type_object = get_post_type_object( $post_type );

	// dont do anything if
	// - not a valid post_type
	// - rewrite not enabled
	// - slug not defined
	// - archive-slug not defined
	// - archive-slug not different from post-slug
	if ( ! $post_type_object || ! is_array( $post_type_object->rewrite ) || ! isset( $post_type_object->rewrite['slug'] ) || ! is_a( $post_type_object, WP_Post_Type::class ) || ! is_string( $post_type_object->has_archive ) || $post_type_object->rewrite['slug'] == $post_type_object->has_archive ) {
		return $permalink;
	}

	// use a cached version written after permalink resave, so we don't have to do grunt work every time.
	$match = get_option( '__wpml_post_type_archive_slug_match', [] );
	$match = $match && isset( $match[ $post_type ] ) ? $match[ $post_type ] : false;
	if ( ! $match ) {
		// sorry, need to save permalinks first.
		// silently fail.
		return $permalink;
	}

	/**
	 * @action wpml_register_single_string
	 * @var string $context the text-domain
	 *                      This should be $text_domain, not $context
	 * @var string $name a description of the string.
	 *                   because this is the actual Context for the string
	 * @var string $value the text to translate
	 * @var bool $allow_empty_value , default = false
	 * @var string $source_lang_code , default to system-default-language.
	 */
	do_action( 'wpml_register_single_string', 'post-type-archive-slug', '', $post_type_object->has_archive );
	$permalink = preg_replace( '@/' . implode('|', $match) . '/@', '/' . __( $post_type_object->has_archive, 'post-type-archive-slug' ) . '/', $permalink );
	/**
	 * Why? sometimes url's come with dual slashes after the website domain.
	 * replace all // with / except when it is ://
	 */
	$permalink = preg_replace('@([^:]/)/@', '\1', $permalink);

	return $permalink;
}, PHP_INT_MAX, 2 );

// above works for "current language" but fails for the language switcher. hence the following hook

/**
 * Part 2: filter the link generation. This works in the language switch.
 * Warning: this is done multiple times during a page generation, but only once for the actual language-switcher
 * This is detected by the code by checking the post_Type being defined. ... ugly, but it works.
 */

add_filter( 'icl_ls_languages', function ( $languages ) {
	$patch            = get_option( '__wpml_post_type_archive_slug_match', [] );
	if ( is_admin() || ! $patch || ! is_array( $patch ) ) {
		return $languages;
	}

	foreach ( $patch as $post_type => $_patches ) {
		$post_type_object = get_post_type_object( $post_type );
		if ($post_type_object && is_a($post_type_object, 'WP_Post_Type')) {
			foreach ( $languages as $language_code => &$language ) {
				$language['url'] = preg_replace( '@/(' . implode('|', $_patches) . ')/@', '/' . ($_patches[$language_code] ?: $post_type_object->has_archive) . '/', $language['url'] );
				/**
				 * Why? sometimes url's come with dual slashes after the website domain.
				 * replace all // with / except when it is ://
				 */
				$language['url'] = preg_replace('@([^:]/)/@', '\1', $language['url']);
			}
		}
	}

	return $languages;
} );

/**
 * Part 3: make the url's work.
 * This step also caches the list of post-types and their possible slugs
 * Effort is mate to only do work when there is actually an archive-slug that is different from the post-type-slug and rewrite is enabled.
 */

add_filter( 'rewrite_rules_array', function ( $rules ) {

	global $sitepress;

	$current_language = $sitepress->get_current_language();

	$post_types = get_post_types();
	$post_types = array_filter( $post_types, function ( $post_type ) {
		$post_type_object = get_post_type_object( $post_type );

		return ! ( ! $post_type_object || ! is_array( $post_type_object->rewrite ) || ! isset( $post_type_object->rewrite['slug'] ) || ! is_a( $post_type_object, WP_Post_Type::class ) || ! is_string( $post_type_object->has_archive ) || $post_type_object->rewrite['slug'] == $post_type_object->has_archive );
	} );
	if ( ! $post_types ) {
		return $rules;
	}

	$languages = apply_filters( 'wpml_active_languages', array(), 'skip_missing=0' );

	$match = array_map( function ( $post_type ) use ( $languages, $sitepress ) {
		$post_type_object = get_post_type_object( $post_type );

		return $post_type_object->has_archive;
	}, $post_types );

	$patch = array_map( function ( $post_type ) use ( $languages, $sitepress ) {
		$post_type_object = get_post_type_object( $post_type );
		$strings          = [];
		foreach ( $languages as $language_code => $language ) {
			$sitepress->switch_lang( $language_code );
			$strings[ $language_code ] = __( $post_type_object->has_archive, 'post-type-archive-slug' );
		}

		return $strings;
	}, $post_types );

	$sitepress->switch_lang( $current_language );

	update_option( '__wpml_post_type_archive_slug_match', $patch );

	$patch = array_map(function($strings){
		return implode('|', $strings);
	}, $patch);
	$match = '@^(' . implode( '|', $match ) . ')/@';
	$patch = '(?:' . implode( '|', $patch ) . ')';


	$keys   = array_keys( $rules );
	$values = array_values( $rules );

	foreach ( $keys as &$key ) {
		$key = preg_replace( $match, $patch, $key );
	}

	$rules = array_combine( $keys, $values );

	return $rules;
} );

xxDocumentation.md

With WPML you can localize the slug of your CPT single, but not your CPT archive, if you give it a different content. This gist will fix that.

With WPML you can localize the "page for posts", but this will not localize the post-URL-base. You can fix this with https://gist.github.com/rmpel/5672b2b943a4a015fe1777c0a31fac59 .

While this will fix all URLs on the front-end, you will still need to fix the Sitemap links, in case you use Yoast SEO (Basic or Premium), or SEO by Rank Math. You van do this with https://gist.github.com/rmpel/b00997f2504c39c718028dfa7e79b87c .

I noticed that the second language archive URL is working on the primary language too.
Now in primary language I have 2 URLs with the same archive. that's weird...