docs: add how to use locale routes

[kenjis]

Description
See #883 (comment)

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[datamweb]

And the way to use the following items does not change?

shield/src/Config/Auth.php

Lines 67 to 72 in 112ba2a

	public array $redirects = [
	'register' => '/',
	'login' => '/',
	'logout' => 'login',
	'force_reset' => '/',
	];

[kenjis]

login is a named route, so not change.