PHP - Changing session value to change the language - php

Question

I am trying to change the session to a value of "en" or "no" by clicking on a link so that the correct language is being displayed on a website.
I have 2 variables, $langNO and $langEN. These are variables containing keys and values of each language.
I am using this:
if (!isset($_SESSION['lang'])) {$_SESSION['lang'] = "en";}
if ($_SESSION['lang'] === "no") {$lang = $langNO;}
if ($_SESSION['lang'] === "en") {$lang = $langEN;}
$lang is related to the strings in the text.
Example:
<h1><?php echo $lang['heading']; ?></h1>
To change the session value, I use this in changelang.php:
session_start();
$_SESSION['lang'] = $_GET['lang'];
header("Location:index.php");
When I click on NO to change the language, it just stays on the default language.
I would love to get some feedback for how this can be solved.
Thank you!

Answer 1

I just changed the index code a little bit
index.php
<?php
session_start();
if (!isset($_SESSION['lang'])) {
$lang = "en";
} else {
$lang = $_SESSION['lang'];
}
switch ($_SESSION['lang']) {
case "en":
$lang = $langEN;
break;
case "no":
$lang = $langNO;
break;
}
?>
NO
changelang.php
<?php
session_start();
$_SESSION['lang'] = $_GET['lang'];
header("Location:index.php");
?>

Answer 2

changelang.php
Set the header() in a function
function redirect(url) {
header('Location: '. url);
}
session_start()
$_SESSION['lang'] = $_GET['lang'];
redirect('index.php');