@NeadReport @jcrabapple

This looks like a link to Youtube's GDPR consent page.

My guess: The preview probably look that way to Vivaldi Social users due to the following sequence:
* Vivaldi Social is hosted on Iceland (a European country)
* The instance will request a preview from Youtube for the link in the post (each separate Mastodon instance requests its own copy of a preview, they are not copied from the original instance).
* The Youtube server will see that the request comes from Europe, and
* does not seem to have previously accepted the GDPR notice, and
* therefore redirects the preview request to the GDPR consent page, and
* since the request comes from and Icelandic IP address ..
* returns the link and title to the Icelandic language version of the GDPR consent page.

This is a particularly difficult problem to solve, because servers have to be located somewhere, and if the website uses the geographical location that requests come from to make decisions about what language to return the resulting page in, it will always end up in the wrong language for someone when generating previews