Why do you need to specify the language in the address bar in a multilingual site if it can be taken from the session?

Question

Internationalization and localization

Why, for example toster.ru/ru/node, specify the language in the address bar, if you can take the client's language from the session?
Here's what I'm doing so far. I determine the language by the client's browser

$lang = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2);

Next, I check if there is a given language in my model, if there is, I write it to the session. If not, I set it to default. The question is - can I do without the language in the address bar, and can it be fraught with what? I will be grateful for advice.
$_SESSION['lang'] = $lang;

Answer 1

At least so that you can follow the link to get to the desired language.