PHP Urlrewriting多个查询参数

Question

I have the problem, that I when I enter this into my browser:

http://localhost/myString

I can get myString by writing $_GET['id']. This works thanks to my following .htaccess file:

RewriteEngine on
RewriteRule ^/?([0-9a-zA-Z]+)$ /myFile.php?id=$1
FallbackResource /index.php

Now I want to add the possibility that users can change the default language. I want this to be possible by entering:

http://localhost/en/myString

myString should be accessible through $_GET['id'] and my language code with $_GET['lang'].

I am completely new to writing .htaccess configs so this is what I tried but didn't work:

RewriteEngine on
RewriteRule ^/?([0-9a-zA-Z]+)$ /chat.php?id=$1
RewriteRule ^/?([a-z]+)$/([0-9a-zA-Z]+)$ /chat.php?id=$2&lang=$1
FallbackResource /index.php