link href="alternative" being created for pages that don't exist

When a page does not have a translation available in a particular language, langswitcher can hide the link from the page.

However, a link to the non-existant page will still be included in the tag in the page header.

Start by tracing the Grav LangSwitcher code that generates the page-header tag, then compare its translation-availability check with the logic that hides the visible language link. Done means the header does not include an alternate link when that translated page does not exist, while available translations still produce links.

Written by the indexing model from the issue text.