From a UI perspective, some form of 'processing' or 'thinking' animation, text, or tooltip after the 'translate' button is pushed and before the translation appears would be useful. Right now, it's not immediately apparent that anything is happening until the translation appears, and that can be several seconds.
This delay, while not an issue in terms of usability, could lead to duplicate button presses or the sense that there is nothing happening even though there is.
Really, anything to convey that the request has been received and is being worked on would be ideal.
