Multilingual site, SEO and redirect | how to proceed?

Question

HTML

Hello.
Interested in such a question.
The site is in several languages, and it is determined from the URL (site.com/ru, site.com/ru/contacts).
Currently, if a user visits site.com or site.com/contacts, they are redirected to their preferred language. And so I wondered if this is acceptable for SEO? Or is it better to remove the redirect and give the user the default site language on these links? What's the best way to do it here? As a result, for example, site.com/contacts and site.com/en/contacts will return the same version of the page.
And another question about the tag

<link rel="alternate" hreflang="x-default" href="http://www.example.com/" />

Is it better to specify the address here without the language and let it be determined on the server side, or specify the address with the default language?

Answer 1

I don't see any problems with the redirect. But with duplication I see