Hi Nicolò,
You have two good certifications and I am sure SAP Project Management certification would be of a great value for you. This one is SAP specific and is more about Solution Manager and ASAP Methodology. Of course, the knowledge of both is mandatory for SAP Project Managers. ASAP is a great methodology that combines project management and ALM methodologies. Solution Manager is the state of art in terms of ASAP methodology automation. I’m a big fan of those two :-)
Because you already have Prince2 Foundation, I would consider taking SAP Project Management certification first and after that Prince2 Practitioner. In my opinion that, and some years of practice, would make you a complete project manager. Of course those who love the profession never stop studying. I’d also recommend you to take a look at PMP certification. In case you also decide for PMP, that would come before Prince2 Practitioner as this compliments PMP (for more details see
http://www.projectsmart.co.uk/pmp-vs-prince2-certificates.php and https://www.prince2.com/prince2-certification-and-pmp).
Best Regards,