In my experience, 'package is in transit to destination country' doesn't necessarily mean that it is actually on a 'plane flying there. What seems to happen is that the package clears Thai customs, outbound, and then waits until a suitable 'plane is available. If you use EMS then the delay is usually short but registered mail seems to take longer.
Again, in my experience, sending stuff to the UK, the package will not reappear on the tracking radar until it has cleared customs inbound at the Langley Postal Centre at Heathrow and this can take several days. Langley has been described as a 'black hole' because things seem to disappear there, sometimes never to re-emerge. Once cleared by Langley it is possible to track the package, either on the Thailand Post website or by using the UK Royal Mail site.
For other destination countries YMMV, as they say.