How do search engines react to a multilingual site?

Question

Search engines

Good afternoon. Please clarify the situation.
I implement multilingualism on the site. At the moment, the logic on the server is as follows:
1) Check if the url contains a variable with a language parameter (for example, site.com/ru/catalog). If there is, then open the page, if not, move on.
2) Check if there is a language identifier in the cookie. If yes, then we redirect from site.com/catalog to site.com/language/catalog, if not, we check further.
3) Automatically determine the user's language, if determined, then do a redirect as in paragraph 2.
4) In other circumstances, do a redirect to the page with the English language (site.com/en/catalog).
So, with this logic, when going to the main page (site.com), we will be redirected to one of the alternative pages (site.com/en or site.com/ru).
The question is how search engines will index the main page of this site, because in fact it does not exist, there will always be a redirect to another one. Perhaps it would be better if, when going to site.com, just open the English version, and place the Russian one in the /ru/ directory, but Google itself advises explicitly specifying the language in the page address. ( https://support.google.com/webmasters /answer/18219...
Thank you.