Most of the countries has only one language and people find it hard to understand this.
It is like English, Chinese, Finnish, French & Russian languages are all in one country.
I can only speak 5 or 6 of them, but thanks to the common language - Pidgin English & Motu, can communicate with most of the people in the country.
If you are happen to be in PNG, ask local people the basic greetings in their own language and try it. If you as a foreigner speak local language, people will really appreciate your effort and Best treatment guaranteed !!