What Does "Multiple URLs referenced for the same hreflang language" Mean?
The URLs have more than one URL listed for a single hreflang language.
Hreflang is a way to tell search engines that there are multiple versions of a page in different languages. This will help search engines serve visitors the most appropriate version of each URL by language or region.
Here's an example of hreflang tags for https://example.com/en-us/products, which is an English page targeting visitors in the United States that also has an English version targeting United Kingdom, a French version, a German version, and a default version available:
<link rel="alternate" hreflang="en-us" href="https://example.com/en-us/products" />
<link rel="alternate" hreflang="en-gb" href="https://example.com/en-gb/products" />
<link rel="alternate" hreflang="fr" href="https://example.com/fr/products" />
<link rel="alternate" hreflang="de" href="https://example.com/de/products" />
<link rel="alternate" hreflang="x-default" href="https://example.com/products" />
In this example, you'll notice that there are no hreflang languages that appear more than once with a different URL. This of course would be confusing if you told search engines that there were 2 or more URLs that should be used for a single language.
Search engines would not know which one to use for this language. Instead, only one URL should be used for a language, so search engines can be very clear about which one to use.
Why It's Important
If hreflang tags are set incorrectly, search engines may ignore the tag completely. If this happens, it's possible search engines will get confused and the wrong version of the page could be ranked in a particular region or language.
For example, visitors from the UK could be served links to the US version of the page on search engines, or visitors from France could be served links to the Switzerland version.
How To Fix
Look at each URL and see all of the hreflang tags on the page. Identify any languages that appear more than once. For each of these, choose which URL is best for this language and remove all other tags for this language.