Site in 2 language without changing the URL, will I have problems with SEO?

Question

I am developing a site in 2 languages in PHP, the first time the user accesses, it takes the browser language with HTTP_ACCEPT_LANGUAGE, if the user changes language, except this choice in a coockie, to follow this language in the rest of the navigation or in future accesses, I believe that this part is right.

My question is in the URL of the site, do I need to change it? How to site.com.br/en (if you access it in English)? Or can I always keep the same URL in both languages? Will I have SEO problems? Google will index the 2 contents?

What is the best way to work, thinking about the SEO side?

Answer 1

I believe the official answer is here:

• https://support.google.com/webmasters/answer/6144055?hl=pt

Google-BOT does not send the Accept-Language, then one should use different urls.

Note that Google in its articles recommends using:

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

So in an article like br.foo.com/1001/seo-site-com-multiplos-idiomas HTML would present something like

<link rel="alternate" hreflang="en" href="http://en.foo.com/1001/bar">
<link rel="alternate" hreflang="de" href="http://de.foo.com/1001/bar">
<link rel="alternate" hreflang="x-default" href="http://www.foo.com/1001/bar">

This is also said on the google link:

Consider adding a replacement page to unrelated languages, especially in language/country selectors or automatic redirect start pages. Use the value x-default:

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

I personally did not want to enter into "debate" on this, but in my view what seems easier (or correct) to the user is simply to present the languages he has and know what are his target audiences and the languages, if the person is from an unlikely language maybe pointing out the article in English would already solve, but I can’t claim 100% (and I’m not talking about SEO, I’m talking about the actual user experience, because this must be the initial concern)