When you have multiple languages on the same site, you need to provide hreflang annotation to show localized pages to correct visitors.
How to Implement the Hreflang
a. HTTP Header (for PDF, Image, etc)
b. Inside the <head> tag (preferred for smaller sites)
c. Sitemap (preferred for larger sites)
Hreflang Best Practices
a. rel=alternate to current URL and version
b. rel=alternate to all lang / lang-region versions (bi-directional).
c. rel=alternate x-default (fallback or if doesn’t match, optional yet good practice)
d. rel=canonical to self reference