Filter language in Polylang for custom taxonomy
Nevermind, I finally found. This is not documented, but going through Polylang code I found a way.
First retrieve the languages with their taxonomy id with
$lang = get_terms('term_language', ['hide_empty' => false])
which gives an object that can be called as
Then, the wp_query should look like this:
$args = array( 'post_type' => ['post', 'page'], 'post_status' => 'publish', 'numberposts' => -1, 'nopaging' => true, 'tax_query' => array( 'relation' => 'AND', array( 'taxonomy' => $taxonomy_custom_category, 'field' => 'name', 'terms' => $taxonomy_term, ), array( 'taxonomy' => 'language', 'field' => 'term_taxonomy_id', 'terms' => $lang->term_id, ), ), );
From there, it’s easy to build a form or whatever you want your plugin to do.
I know this is a bit off topic, but this information is unavailable anywhere. I nevertheless found that many plugin developers are getting stuck as I was.