While you're right we haven't built a UI specifically from our phone UI for tablet, there are
optimizations in there for tablet – they are just more subtle in terms of font-sizes, button sizes, etc. Stay tuned though, we hope to in the future have a UI that is truly stunning for tablet as well.+Sérgio Pereira
While it may not be quite what you're asking for, you can Share
with the Translate app from other Android apps that give you the option to share their content. I use this frequently in Gmail, where you can select text, and then Share
with other apps (this at least works on ICS).