What triggers this issue?

This issue reports pages referenced for more than one language in hreflang annotations.
E.g.
<link rel="alternate" hreflang="en" href="http://webbsite.com/page.html" />
<link rel="alternate" hreflang="de" href="http://webbsite.com/page.html" />

Why is it important?

Hreflang helps search engines to point users to the most appropriate version of your page, depending on users' language and region.

Annotations, where different languages are announced for one page, may be ignored or not interpreted correctly.

How to fix it?

Make the necessary changes on the pages that send hreflang links to the reported URLs. One language version of a page must be referenced for one language only. You can, however, assign multiple locations with the same language in hreflang values to one URL, e.g. en-us, en-gb, etc.

You can get the list of pages that link to the URL from their hreflang annotations by clicking on the number in "No. of hreflang inlinks" column.

Example:

Google's guideline to hreflang implementation.

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