Send WPML preferred language to Mautic

mautic-wpml-lang.php

<?php
/*
Plugin Name: Mautic WPML Preferred Language
Plugin URI: https://www.robertwent.com/
Description: Sends WPML language preference to Mautic
Version: 1.0
Author: Robert Went
*/

function mautic_wpml_lang_init() {

    // Only run for known users on the frontend
    if (is_user_logged_in() && !is_admin()) {

        // The var needs to be global to be able to get the value in the filter
        global $user_locale;
        // Check if the user has set a preferred locale
        $current_user = wp_get_current_user();
        $user_locale = get_user_meta( $current_user->ID, 'locale', true ); 

        // Only call the filter if there is a value set
        if ($user_locale) {

            add_filter('wpmautic_tracking_attributes', function($attrs) {
                // Access the variable set outside the function
                global $user_locale;

                // Attach the lang to the attributes array
                $attrs['preferred_locale'] = $user_locale;

                // Return the new array to the main plugin 
                return $attrs;
            });

        } 

    }

}

// We use the init action as plugins run too early by default to check if a user is logged in
add_action('init', 'mautic_wpml_lang_init');