It seems that when it comes to hreflang implementation, (according to SEMrush in 2017) 75% of websites that integrate it have been having implementation errors.

More recently, Dan Taylor did a study of almost 2000 Salesforce Commerce Cloud websites and found that 63% of them that had hreflang implemented contained errors.

This information is pretty scary, especially if your branded website is meant to be multilingual. The last thing you want is somebody who only speaks a particular language your claim to support, and they can’t read it because of a simple implantation error.

in a column by Dan Taylor, he will show us the different facets of a multilingual website that you’ll want to plan for, how to structure hreflang tags, and how to implement your hreflang strategy.

Read more here on Search Engine Journal