What is the best way to implement multilingualism regarding SEO?

Question

Search Engine Optimization

Content in Russian and English, essentially the same - with the same materials, translated manually.
A link to an alternative version (another language) is located in the footer on all pages.
What is the best way for SEO to implement such a multilingual division in terms of domain-
1) ru.site.com and site.com
2) site.com/ru and site.com/en
3) site.ru and site.com (on the same server)
How to make it not be considered a repetitive material or an affiliate (in the third case, and, accordingly, some query keys will match, such as English-language brand names for example)? Or is everything the same in order and the search engines will figure it out themselves?

Answer 1

Personally, I would do site.com/en/ site.com/ru/ etc.
On pages, I would specify the hreflang attribute for cross-language links, and the lang attribute is also required in the document title.
In such a scheme, the weight of the domain will increase due to each link to it. Plus there are conveniences like SSL/TLS etc.