@rmondello The short URL youtu-dot-be doesn’t provide OpenGraph data, so… no previews.
☝🏻 This little detail came across my feed recently and now I can’t find it to credit the original author. 🙃
The advice from that post was to avoid using YouTube’s share/embed UI and instead copy the video page’s URL from your browser’s address bar.
…and, a relevant reply that Ricky’s boosted:
@[email protected] Youtube recently made a change and stopped serving the video pages when Mastodon (or other software, AFAIK) is requesting it, probably using some fingerprinting. Mastodon builds a link preview based on the page that is served, hence what you are seeing (in German because your server is probably located in a datacenter in Germany, or Youtube thinks it should see german language). We tried to get in touch with people at Youtube, but no success so far.