>> because the English option is at the top of the list and is off screen
Looks like this was fixed in the Nov 11 update. Accessing the English option at the top of the menu works OK for me now.
https://community.adobe.com/t5/Community-Feedback/November-11th-Release-Notes/td-p/10739478
"Bug: Translation menu should no longer show above button and should no longer hide the English option."
However, no error message appears when the Subject language = target translation language but the body text still requires translation. In that case now, the Translation option just does nothing. I preferred the error message. At least we knew what was going on then.
Surely all they need to do is extend the script fired by the Translate button to check the language for both Subject and body? Or ignore the Subject entirely and check the body text?