Uncle Sam refers to it as a
license too.
It is not abbreviated as PPC. That wouldn't be clear. The FAA always aims to be as clear as possible. So they spell it out : "private pilot certificate".
Licence is the UK spelling. The UK does not have a prerogative to impose English language spelling across Europe. License can be just as European. As a matter of fact, our beloved EASA spells it as "License".