The nation is said to be in the middle of a civil war or a war for independence (presumably from Indonesia), with mercenary rebels for hire. Roberto Rastapopoulos's hired gun, Allan Thompson, recruits Sondonesians as gun carrying muscle in Flight 714. They appear to be based on Khmer Rouge or East Timor freedom fighters. Hergé's insistence that Sondonesia is in a state of civil war shows amazing clarity of vision of the true state of conflict in Cambodia during that period.
The name Sondonesia is a portmanteau of Sunda and Indonesia. The inclusion of Jakarta's Kemajoran airport and the radio message from Makassar just before the plane is hijacked suggests that the location is not far from the Malay/Indonesian archipelago, likely between Indonesia and Australia (since the Carreidas 160 is said to have gone missing missing between Makassar and Darwin). The Proboscis monkey which appears later in the album is exclusive to Borneo.
Sondonesian conversations (such as the angry sailor on the boat, and the two bunker guards) in the album are spoken in Indonesian Malay. Translations of the dialogues can be seen at 
- Sondonesia in the Tintin series is a fictional country.