Hacker news isn't "fully selectable". Just try to highlight the text in the reply/update/submit buttons.
I am curious what operating system you can select text from the buttons on though. I might spin up browserstack to experiment.
This is what is copied from the login page, you can see that the button text is missing:
Login
username: password:
Forgot your password?
Create Account
username: password:
But yeah, HN isn't the best in this regard :)
Maybe dang will one day consider changing to <button>reply</button>!
You can highlight the buttons (most times) in Safari on MacOS, but you can't select the text and copy it or translate it.
<input value="reply" type="submit">