ElasticPress WPML Sync Issue

For anybody else landing here with this problem, WPML now adds a post_lang attribute the posts' mappings. (I'm using 3.9.4)

It also adds a post_filter argument to the request itself so it considers this post_lang in ElasticPress queries.

One problem remains : the indexing is still for a unique language as described in this issue.

To resolve this, add a filter to suppress WPML's filter on the indexing

add_filter('ep_index_posts_args', function($args) {
    return array_merge($args, [
        'suppress_filters' => true,
    ]);
});

https://github.com/10up/ElasticPress/issues/477