What is the technical term for this corner cupboard?
I am not certain what you mean by a "technical term" for it.  I would call it a corner hutch or a corner display hutch or maybe a corner bookcase.

Why corner? Because it is shaped to fit in a corner.

Why hutch? A hutch is sometimes something that sits on top of a bureau, table, desk, or other piece of flat-topped furniture. However, hutches can also be a free-standing shelved storage units with doors.  The impression people have of "hutch" will vary by region.

Why bookcase? It's got books on it.

I can tell you also that I would not call it 


a cabinet: Cabinets usually have doors and are wall-hung or sit on the floor.
a cupboard: Cupboards are usually wall-hung and contain dishwares or foodstuffs
a curio cabinet: these usually have mirrored backs and glass doors
a display case: see curio cabinet. These usually have at least glass doors.