سلام
اگر تغییر زبان از طریق آدرس سایت انجام بشه، موتورهای جستجو می تونند زبان های دیگه رو ایندکس کنند، اما اگر از طریق سشن و کوکی و ... باشه تا جایی که من اطلاع دارم به خوبی قابل ایندکس نیست.
https://support.google.com/webmaster...r/182192?hl=en
Use different URLs for different language versions
Google recommends using different URLs for each language version of a page rather than using cookies or browser settings to adjust the content language on the page.
If you use different URLs for different languages, use hreflang annotations to help Google search results link to the correct language version of a page.
If you prefer to dynamically change content or reroute the user based on language settings, be aware that Google might not find and crawl all your variations. This is because the Googlebot crawler usually originates from the USA. In addition, the crawler sends HTTP requests without setting Accept-Language in the request header.