Not the easiest to implement, but when translate a word, I sometimes would like to have some extra information : grammatical gender or group, accentuated syllable, declination, pronunciation…
As your tool is also design to translate a full sentence, maybe these information should appear only when mouse is over a single word. It could be based on the wiktionnay database for example.
Of course this is not a trivial add, so I understand if this is not your priority. But I drop the idea here, just in case one day…