Create a REST endpoint for WordPress, providing a list of user newsletter subscriptions (email and language for each)

newsletter-subscriptions-rest-endpoints.php

<?php
/*
Plugin Name: Helper Plugin - Newsletter Subscription REST endpoints for WP PoP API 
Version: 0.1
Description: It creates a REST endpoint to demonstrate the PoP API
Plugin URI: https://gist.github.com/leoloso/c14f74ca26eced8bc6e71ba161d672c4
Author: Leonardo Losoviz
*/
if (function_exists('add_action')) {
  add_action('rest_api_init', 'register_newsletter_subscriptions_endpoint');
}
function register_newsletter_subscriptions_endpoint()
{
  register_rest_route('newsletter/v1', 'subscriptions/', [
    'methods'  => 'GET',
    'callback' => 'get_newsletter_subscriptions'
  ]);
}
function get_newsletter_subscriptions($request)
{
  $langs = ['en', 'es', 'fr', 'de'];
  $users = get_users(['number' => 12, 'role' => 'subscriber']);
  $userdata = [];
  foreach ($users as $user) {
    $userdata[] = [
      'email' => $user->user_email,
      'lang' => $langs[$user->ID % 4],
    ];
  }
  $response = new WP_REST_Response($userdata);
  $response->set_status(200);
  return $response;
}