A simple routing function with i18n json data

i18n.php

<?php

define('i18n', dirname(__DIR__) . '/locales/');

function __($phrase) {
    $locale = $GLOBALS['APPLANG'];
    static $trans = NULL;
    $ext = '.json';
    if (is_null($trans)) {
      $lang_file = i18n . $locale . $ext;
      if (!file_exists($lang_file)) {
        $lang_file = i18n . $locale . $ext;
      }
      $lang_file_content = file_get_contents($lang_file);
      $trans = json_decode($lang_file_content, true);
    }
    // return var_dump($trans[$phrase]);
    return $trans[$phrase];
  }

session.php

<?php

function is_session_started()
  {
    if ( php_sapi_name() !== 'cli' ) {
      if ( version_compare(phpversion(), '5.4.0', '>=') ) {
        return session_status() === PHP_SESSION_ACTIVE ? TRUE : FALSE;
      } else {
        return session_id() === '' ? FALSE : TRUE;
      }
    }
    return FALSE;
  }

  if ( is_session_started() === FALSE ) {
    session_start();
    $available_langs = array('en','tr');
    $_SESSION['lang'] = 'tr';
    if(isset($_GET['lang']) && $_GET['lang'] != ''){
      if(in_array($_GET['lang'], $available_langs)) {
        $_SESSION['lang'] = $_GET['lang']; // Set session
      }
    } else {
      $GLOBALS['APPLANG'] = 'tr';
    }
    $GLOBALS['APPLANG'] = $_SESSION['lang'];
    $GLOBALS['i18n'] = '?lang=' . $GLOBALS['APPLANG'];
  }

url.php

<?php

function route($req)
  {
    require_once dirname(__DIR__) . '/web.php';

    $req_file = $routes[$req] . '.php';
    $url = parse_url($req);

    if (is_readable($req_file)) {
      include_once $req_file;
    } elseif ( strpos($req, $GLOBALS['i18n']) ) {
      $req = $url['path'];
      include_once $routes[$req] . '.php';
    } else {
      echo "404: File name " . $req . " could not be loaded";
    }
  }

web.php

<?php

  $routes = [
      '/' => dirname(__DIR__) . 'pages/index',
      '/about' => dirname(__DIR__) . 'pages/about',
      '/sub/page' => dirname(__DIR__) . 'pages/sub/page'
    ];