Create your hreflang link-attribute markup for your multi-language website while keeping the bi-directional nature of the links in mind. All equal content needs to be interlinked or Google may consider the markup broken.
Please add this code into the head part of each page you defined in the href-attributes:
The hreflang-guide for international SEO
In this guide we will show you how to correctly handle multi-language websites when it comes to Google. Avoid duplicate content and learn how to use the hreflang link-attribute.
The language for this document is German (de) and is designated for the Region of Austria (AT). Thus, the content on www.domain.de/at/ is marked for German speaking users in Autria.
The language (de) needs to use the ISP 639-1 format. The regional-code (-AT) is optional and has to use the ISO 3166-1 Alpha 2 format.
The ISO-code ist not case-sensitive. Google will also accept lower case mentions of the optional regional-codes. The hreflang link-attribute markup will still be valid.
Keeping with the conventions, however, by writing the ISP-code for the language in lower-case and the optional regional ISO-code in upper-case is prefered.
What is the correct way of using the hreflang-markup?
When you use the hreflang-markup it is important to keep the bi-directional nature of the links in mind. This means that all equal content needs to be linked between each other. If the hreflang-markup is set up in "one direction" you will have broken the structure and Google will consider the markup invalid.
Every piece of content is referencing the other pieces of content, respectively (bidirectional links).
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