I want it to be a translator with voice-recognition - ANY speaker talks into The Hand, and out pops the appropriate translation. I had that on a Palm Pilot in the late '90s but it was limited to one speaker who 'voice-trained' it on words, and its translation library was less than my own! I wanted to plug in Polish or Mandarin or Thai or Basque, but nooooo... "library not available."
The watch-as-translator would be lessened then because of its size - if it could only offer readable-word translations, then the size of that display needs to be much larger than 4- or 8-characters' width.
Well, maybe that's iWatch II. Or III. Er, Ap-Ap-Apple Watch...