How to correctly build a URL for a multilingual site?

Question

Search Engine Optimization

As far as I know, there are several ways to implement multilingualism with their pros and cons:
1. Implementation through a domain / subdomain. For example, site.ru is Russian, en.site.ru or site.com is English. Here, I think, there are no problems from a technical point of view and from an SEO point of view. The only negative may be that these are completely different sites and, accordingly, it can be problematic to indicate that this is the same site for the PS.
2. Implementation via URL: For example, site.com/ru or site.com/ru-ru and site.com/en or site.com/en-us. I consider the construction of the entire architecture within one domain as the advantages of such an implementation, and almost all pages have their analogue (ideally) in another locale. But here, for SEO, the question arises that there is no that very main site.com page, since it redirects to the recognized user locale ("/" -> "/ru" for example). Of course, you can solve this with a "crutch", that the main one is only for the "main" language without parameters and redirect accordingly ("/ru" -> "/"), but my inner perfectionist suffers madly with this option, because it's still a "crutch" ". If you specify such sites as microsoft in the arguments, then in response you can hear something like "
3. Similar to p2, only use the GET parameter - site.com - Russian, site.com/?lang=en - English. To be honest, I don't like this option at all, since it's generally wrong to make "permanent" pages with a GET parameter.
4. All pages by their URL are available in all locales and run in the one that is determined when reading the titles. Here you can use several options for determining: Accept-language, GeoIP, locale from settings if authorized, default locale. But even in this way, it turns out that for a search engine, one URL can theoretically be displayed with different content, which is highly undesirable from an SEO point of view. Although I consider this method the most user-friendly.
So how can you properly organize the construction of multilingualism on the site so that everyone is happy?

Answer 1

so, the correct answer is site.com/en
The link to the site should look like site.com
Determining the language to redirect to in the order of checking:
1) cookies (perhaps the person has already been to you and selected the language)
2) Accept-language, i.e. to. most still put their native locale in the browser.
3) GeoIP if for some reason the above points didn't work
4) Default language (presumably the most common for your audience) as the ultimate truth.
As such, there will be no MAIN page, but this is normal for any multilingual site, Google considers this to be an adaptation for the client, i.e. "a site for people", everything is ok here.

Answer 2

site.com/enlike most (for example, Microsoft).

Answer 3

Option 3 is what you don't like. And the language is passed through a cookie, the GET parameter has priority.
In the title of the page write:

<link rel="alternate" hreflang="x-default" href="http://site.com/" />
<link rel="alternate" hreflang="en" href="http://site.com/?lang=en" />
<link rel="alternate" hreflang="ru" href="http://site.com/?lang=ru" />