Does a wordpress custom plugin is fired by default on php theme ajax request?

Question

Inside My custom wordpress plugin to translate all posts depending on get_locale() I created a php file that's add_filter() to each post content element.

Ajax requests are called from functions.php and depending php files inside themes folder.

My php code works fine for all page loaded without Ajax. I want to allowed my plugin to be load before all ajax call/request. I don't know if I have to hook wp_ajax_() inside my php plugin or if an other solution exist or if I've forgotten to apply a wp function when I call ajax so that any plugin can be read automatically.

my typical php ajax :

add_action('wp_ajax_nopriv_filter_date', 'filter_ajax_date');
add_action('wp_ajax_filter_date', 'filter_ajax_date');

function filter_ajax_date(){
    "my wp_query"
    wp_reset_query();
    wp_die();
}

When I click on button "date filter" I load posts from other date period using ajax filter_ajax_date function.

At the end of "my code" I tried to use alone : if( wp_doing_ajax() ) {} and with 'add_action' from this code:

add_action( 'admin_init', 'my_ajax_checker', 10, 2);

function my_ajax_checker() {
    if( wp_doing_ajax() ) {
         add_action('plugins_loaded', 'atv_convert_multilingual');
    }
}

No one works.

My code (my-plugin/includes/multilingual-query.php):

function atv_convert_multilingual(){

    if(!is_admin() ){       
        add_filter('the_title','atv_translate_title',10,2);
        add_filter('the_content','atv_translate_content',7);
        add_filter('get_the_excerpt','atv_translate_excerpt',9,2);
        add_filter('get_post_metadata', 'atv_translate_meta_subtitle', 10, 4);
        add_filter('get_post_metadata', 'atv_translate_meta_forwho', 10, 4);
    }

    function atv_translate_lang_post($post_object, $object_id, $whichelement, $metaform = null, $meta_key = null){}

    function atv_translate_title($title, $object_id){
        $whichelement = 'title'; $post_object = $title;
        return  atv_translate_lang_post($post_object, $object_id, $whichelement, null);
    }
}
add_action('plugins_loaded', 'atv_convert_multilingual');

For debugging purposes and to avoid my bad practices, here is the function to retrieve the content of the post/postmeta will be modified using add_filter :

function atv_translate_lang_post($post_object, $object_id, $whichelement, $metaform = null, $meta_key = null){

    if ( 'liste_associations' == get_post_type()) {
        $englishforalllang = 'en_GB';               
        if(get_locale() == 'fr_FR'){
            return $post_object;
        }elseif(get_locale() != 'fr_FR' || get_locale() == $englishforalllang ){
            // For POST meta
            if(isset($meta_key) && $metaform == $meta_key){
                $ifposthasmetalang = '/^_[a-z]{2}_[A-Z]{2}$/'; 
                $meta_id = get_post_meta($object_id);
                foreach($meta_id as $metakey => $metaval){
                    if(preg_match($ifposthasmetalang, $metakey)){
                        if($metakey ==  '_'.$englishforalllang || $metakey != '_'.$englishforalllang ){
                            $datalang = get_post_meta( $object_id, $metakey, true );
                            $langcontent = unserialize(base64_decode($datalang));
                                        
                            $post_object = $langcontent[$whichelement];
                        }
                    }
                }
            }
            // For POST elements
            if(!isset($meta_key) && !isset($metaform)){
                $ifposthasmetalang = '/^_[a-z]{2}_[A-Z]{2}$/'; 
                global $post;
                if($whichelement == 'title' || $whichelement == 'content'){
                     $meta_id = get_post_meta($object_id);
                }elseif($whichelement == 'excerpt'){
                    $meta_id = get_post_meta($post->ID);
                }
                foreach($meta_id as $metakey => $metaval){
                    if(preg_match($ifposthasmetalang, $metakey)){
                        if($metakey ==  '_'.$englishforalllang || $metakey != '_'.$englishforalllang ){
                            if($whichelement == 'title' || $whichelement == 'content'){
                                $datalang = get_post_meta( $object_id, $metakey, true );
                            }elseif($whichelement == 'excerpt'){
                                $datalang = get_post_meta( $post->ID, $metakey, true );
                            }
                            $langcontent = unserialize(base64_decode($datalang));
    
                            $post_object = $langcontent[$whichelement];
                                            
                        }
                    }
                }
            }
            return $post_object;
        }
    }
  }

Answer 1

This will never work:

add_action( 'admin_init', 'my_ajax_checker', 10, 2);

function my_ajax_checker() {
    if( wp_doing_ajax() ) {
         add_action('plugins_loaded', 'atv_convert_multilingual');
    }
}

This is because by the time admin_init runs, plugins_loaded has already happened! Making this code would would require the code to travel backwards in time.

Instead it would be much simpler to do this:

add_action('plugins_loaded', 'atv_convert_multilingual');

Or this:

if( wp_doing_ajax() ) {
     add_action('plugins_loaded', 'atv_convert_multilingual');
}

Take a look at https://www.rarst.net/wordpress/wordpress-core-load/ for more information on the order that hooks fire in WordPress