Support Polylang

Hi! This is an amazing plugin which we use almost in every site, thanks!

There are a few things that are bugging me, related to compatibility with Polylang:

- CPT archive page slugs need to be translated in Polylang "Strings translations" tool to exactly same as the translated archive page slug is. I'd like to find a robust solution for this, or at least give the user a reminder about this
- menus do not get `current-menu-item` etc classes for translated archive pages, I have a small workaround for that to be put in `filter_wp_nav_menu_objects` function after `$page_ids` is set

```php
if ( function_exists( 'pll_current_language' ) ) {
if ( pll_current_language() !== pll_default_language() ) {
foreach ( $page_ids as $tmp_page_id_key => $tmp_page_id ) {
$page_ids[ $tmp_page_id_key ] = pll_get_post( $tmp_page_id );
}
}
}
```

I'm wondering, do you accept PR's for this kind of compatibility issues or should I create a plugin for Polylang compatibility?

Start by reviewing the plugin's filter_wp_nav_menu_objects function and the Polylang functions shown in the issue. Reproduce the translated CPT archive and menu behavior, then determine whether both translated slugs and current-menu-item classes can be supported. Done means an agreed compatibility behavior is implemented or the limitation is clearly documented.

Written by the indexing model from the issue text.