Allesandro, Pootle does not yet support TM, but I know some people have used its terminology feature to include longer phrases.
If you are interested in TM and automated translation, I would run this from the offline tool like KBabel or PoEdit and import the PO files to Pootle later. Friedel, do you think TM functionality will be added to Pootle anytime soon? Regards, Aiet