Google Webmaster Tools is complaining about the missing hreflang attributes on our Nopcommerce webshop. We have a two-language setup. According to this guide https://support.google.com/webmasters/answer/189077?hl=en our case is the third listed: '•Your site content is fully translated. For example, you have both German and English versions of each page.'
Please someone explain if this is really needed for better SEO results (at least in one of the languages), and how to setup (or add in source code if this feature is missing in Nopcommerce) the proper hreflang tags to our site.