This last post doesn’t show the translate button. Is there anything that can be done about it?
I fear the most you can do is ask the author to try to explain it in english.
Or report a bug to the author of the discourse plugin.
I think the feature does not work well when the post starts with a quote. I guess it is because it can not deduce the language of the post. I filled https://meta.discourse.org/t/missing-translation-button/180373.