For more precision:
I'm runnning Ubuntu 12.04
I'd like an indicator which shows up to the left of the date/volume/wifi icons
If possible I'd like to be able to change the translation language
The indicator could use internet based translators (google translate etc.) or have a complete library come with it so translations can be obtained offline.
Relating to usability: I'd like to have it work in a way where you click on the indicator icon and you can start typing either directly or once a window has opened and it instantly shows the translation you need (with your target languages pre-set or determined in options).