Cosmo Multilingual Kit for Polylang

Polylang free covers the basics. Building a real multilingual theme on it, you quickly run into things that only Polylang PRO or WPML handle. This plugin adds them, configured from your theme in code so the setup travels with the theme rather than the database.

• The same slug in every language. /about-us/ and /es/about-us/ instead of /es/about-us-2/, for posts, pages, custom post types and terms. Requests resolve to the post or term of the requested language.
• Translated URL bases. /success-stories/ in English, /es/casos-de-exito/ in Spanish, for post types, taxonomies and the blog base.
• Per-language ACF / SCF options pages. Language tabs above the options page, a “copy from the default language” button, and a fallback to the default language for empty values. get_field( 'name', 'options' ) keeps working.
• Duplicate as translation. A “Duplicate → Español” row action copies blocks, custom fields, featured image, template and terms, and links the posts as translations.
• Copy from another language. A “Translation” box in the editor replaces a translation’s title, content, custom fields and terms with those of any other language, like WPML’s “Copy content from”. New translations created with Polylang’s “+” start pre-filled from the source post.
• Outdated translations. A translation remembers what it was copied from. Once the source changes, the editor box and the posts list flag it as outdated until it is marked up to date or copied again.
• Menu sync. One button on the Menus screen copies the default language menus to every other language and assigns them to the same locations. Items point to the translated posts and terms, labels already translated are kept, and items removed from the source are removed from the copies.
• Translated ids on output. Reusable blocks and ACF post object, relationship and taxonomy values, options pages included, show the current language’s translation when there is one.
• Default category in every language. Repairs the default category translation Polylang leaves without a language when languages are created programmatically, and creates missing ones.
• Image alt per language, with a fallback to the library alt, for images output with wp_get_attachment_image(). The block editor’s Image block saves its alt into the post content and is translated with the post.
• Theme strings in Languages → Translations.
• Author profile fields per language, including the biography fallback Polylang free lacks.
• Language switcher data that hides untranslated, hidden or not-yet-translated copies, or keeps them greyed out, plus hreflang x-default.
• Untranslated front page. Until the static front page is translated, a language’s home redirects to the default language one instead of showing its empty blog, home links follow, and hreflang leaves that language out. Hidden languages are left out of hreflang too.

Requires Polylang 3.7 or later.

Cosmo Multilingual Kit for Polylang is an independent, unofficial plugin. “Polylang” is a trademark of WP SYNTEX; this plugin is not affiliated with or endorsed by WP SYNTEX, and the name refers to that plugin solely to describe what this one works with.

Configuration

Everything is configured through a single filter, typically in the theme’s functions.php:

add_filter( 'cosmo/multilingual_kit/config', function ( $config ) {
    return array_merge( $config, [
        'post_types'       => [ 'post', 'page', 'story' ],
        'taxonomies'       => [ 'category', 'post_tag', 'story_category' ],
        'bases'            => [ 'blog', 'story', 'story_category' ],
        'base_map'         => [ 'story' => [ 'es' => 'casos-de-exito' ] ],
        'options_pages'    => [ 'site-options' ],
        'strings'          => [ 'read_more' => 'Read more' ],
        'strings_group'    => 'My theme',
        'user_fields'      => [ 'position' => 'Position' ],
        'pending_meta'     => 'translation_pending',
        'hidden_languages' => [ 'uz' ],
    ] );
} );

• post_types, taxonomies — made translatable in addition to Polylang’s settings.
• bases — sections whose URL base can be translated: post type names, taxonomy names, or blog. A default can be given explicitly ('blog' => 'news'), otherwise the registered rewrite slug is used. Every URL of the section follows the translated base: nested terms, feeds, paging, archives.
• base_map — translated bases per language. Flush permalinks after changing it, and let your SEO plugin rebuild its URL cache.
• options_pages — ACF options page slugs stored per language. Storage goes by the page’s post id, so every options page that keeps the default options post id becomes per-language too; give pages that should stay shared their own post_id. A field left empty in a language shows the default language value, except for cells inside repeaters and flexible content.
• strings, strings_group — template strings registered with Polylang.
• user_fields — profile fields translated per language.
• pending_meta — meta key set on duplicated copies; while set, the language switcher hides that language.
• hidden_languages — languages left out of the switcher and hreflang, e.g. while their content is being prepared.
• x_default — add hreflang x-default (default true).
• prefill_translations — pre-fill translations created with Polylang’s “+” from the source post (default true, off with Polylang PRO, which does it itself).
• modules — switch modules off: [ 'media' => false ]. Keys: slugs, bases, default_term, options, duplicate, translations, menus, ids, media, strings, users, frontend.

Template functions

• cosmo_mlk_language(), cosmo_mlk_default_language(), cosmo_mlk_locale( $language ), cosmo_mlk_languages()
• cosmo_mlk_home_url( $path, $language ), cosmo_mlk_url_prefix( $language ), cosmo_mlk_url_base( $key, $language )
• cosmo_mlk_switcher( $args ) — languages for a switcher: slug, name, locale, url, flag, current, available. Pass keep_unavailable => true to keep untranslated languages with an empty url.
• cosmo_mlk_t( $key, $fallback ) — translated template string
• cosmo_mlk_user_field( $user_id, $key, $language ), cosmo_mlk_image_alt( $attachment_id, $language )
• cosmo_mlk_translated_post( $post_id, $language ), cosmo_mlk_readable_translation( $post_id, $language ), cosmo_mlk_pending_translations()
• cosmo_mlk_term_by_slug( $slug, $taxonomy, $language ), cosmo_mlk_insert_term( $name, $taxonomy, $language, $args )
• cosmo_mlk_duplicate_post( $post_id, $language, $args ), cosmo_mlk_link_translations( $map ), cosmo_mlk_link_term_translations( $map )
• cosmo_mlk_copy_post( $from, $to ), cosmo_mlk_translation_outdated( $post_id )
• cosmo_mlk_sync_menus()
• cosmo_mlk_copy_options( $from, $to, $pages ), cosmo_mlk_migrate_legacy_options( $language )

Every function keeps working with Polylang switched off, falling back to a single default language.

Hooks

• cosmo/multilingual_kit/config — the configuration above.
• cosmo/multilingual_kit/switcher — filters the switcher language list.
• cosmo/multilingual_kit/duplicated — fires after a translation is created by copying: ( $new_id, $source_id, $language ).
• cosmo/multilingual_kit/copied — fires after an existing translation is overwritten from another language: ( $post_id, $source_id, $language ).