Link related topics using link-tag for better helping search engines

On our forums we have segmented Dutch and English across a range of categories. Each category has a primary language and moderators make sure the content is moved when landing in the wrong language’s category.

For the content written in wiki’s, there is often a need for an English and Dutch version. Therefore, for each language content is developed and put online. Example:

This Dutch content has an English variant with similar information for an English-reading user population:

The two topics are linked for user navigation (and workarounds for SEO issues on Bing and Google, see Missing HTML meta-tag "Content-Language" for BING language detection and Language support on category level for more relevant search results) by a hyperlink at the start of the text: “Go to LANGUAGE version”

However, there is currently no structured way in Discourse to tell search engine that two topics actually serve the same information but in a different language. This makes it harder for search engines to present content in the searcher’s language, plus each individual page has to build it’s own page authority, instead of them being summed together.

On another site we therefore have on each page (and sitemaps) included link-HTML tags to help search engines understand the structure as documented on Localized Versions of your Pages | Google Search Central  |  Documentation  |  Google Developers :

<link rel="alternate" hreflang="nl" href="" />
<link rel="alternate" hreflang="en" href="" />
<link rel="alternate" hreflang="de" href="" />
<link rel="alternate" hreflang="fr" href="" />
<link rel="alternate" hreflang="es" href="" />
<link rel="alternate" hreflang="it" href="" />
<link rel="alternate" hreflang="da" href="" />
<link rel="alternate" hreflang="nb" href="" />
<link rel="alternate" hreflang="sv" href="" />
<link rel="alternate" hreflang="fi" href="" />
<link rel="alternate" hreflang="pt" href="" />
<link rel="alternate" hreflang="ja" href="" />
<link rel="alternate" hreflang="x-default" href="" />
<link rel="canonical" href="" />

This is not uncommon, such as Apple does:

<link rel="alternate" href="" hreflang="en-US" />
<link rel="alternate" href="" hreflang="ar-AE" />
<link rel="alternate" href="" hreflang="en-AE" />
...a stunning 140 languages...
<link rel="alternate" href="" hreflang="en-VN" />
<link rel="alternate" href="" hreflang="en-ZA" />
<link rel="alternate" href="" hreflang="zh-CN" />

It would be helpful when topics could be linked to instruct search engines for their structure. This could include language links like above on alternate.