It seems that the "Beatbox" button is created after the page load, probably by some Ajax call. That may explain why some people are not seeing it.

I don't see any "Beatbox" button, it says "Listen".

On the left, under the text input box.

Screenshot: http://i.imgur.com/4jd5y.png

The "beatbox" link is absent for me, and the "listen" link is present but doesn't work for me. shrug

The "Beatbox" button is under the untranslated text (that is supposedly in German).

It's easier to see if you set it to translate German -> German, because then both listen buttons will become beatbox buttons.