To get worldwide privileges (VFR, noncommercial) you need a license which was issued by the same country as the aircraft is registered in.
The above applies to ICAO licenses, and aircraft with ICAO certificates of airworthiness.
If the above requirements are not complied with, all bets are off. For example the UK NPPL is not ICAO compliant and is thus unrecognised (outside the UK). There are other such licenses, in the far corners of the world.
However there are also concessions, which deliver privileges additional to the first paragraph above. For example you can fly a G-reg plane on any ICAO license (again, noncommercial VFR).
But there are very few of these automatic validations. JAA is the biggest one; it is an arrangement for mutual license validation, where by any JAA PPL is good for any plane registered in JAA-land.