ah, I get it now. thanks for explaining.
can I ask what the purpose of the other iframe is? it seems to want to translate to English? But if the input language is English what is the idea? and why not fire the function on the onkeyup of the textarea the way you do with the first iframe?
also, this is going to cause you problems:
there is, sadly, I believe, no body onhaschange event, and the equivalent is hard to implement in a cross-browser fashion.
innerText will get you into trouble, too. innerText is IE only. textContent is more widely accepted, but IE only started recognising it at IE9+
if you are only looking to translate the text from the textarea, it is much easier just to be getting the value of that textarea, the same as you are doing now.