I'm currently working on a multilanguage website and I need it to be SEO optimalized. I support the dutch, english and american-english language/location. I have a couple of questions about the optimalization.
<link rel=”alternate” href=”http://www.example.com/” hreflang=”x-default” />
You already separate your page content for different languages using different language URLs. This is recommended because you are not having multiple versions of the same URL, but with different content (if you were to use only sessions for example, and would show the same page in different languages).
I add hreflangs to my multilingual site, as per Google recommendation. I suggest you do the same.
From Google docs https://support.google.com/webmasters/answer/189077?hl=en :
If you have multiple language versions of a URL, each language page must identify all language versions, including itself.
So on every page, you specify hreflangs for all versions of that page in your different languages.
Let me give you an example from my web application, that supports 2 languages ru and tk. For ru I do not specify lang in the URL, for tk language, /tm/ is added to URL. If you go to https://www.tmawto.com/cars you will see the following meta:
<link rel="alternate" hreflang="ru" href="https://www.tmawto.com/" /> <link rel="alternate" hreflang="tk" href="https://www.tmawto.com/tm/" />
It goes the same for all pages. For each page you specify hreflang version in all other languages. No need for additional HTTP header.