A Christian missionary from PNG explains how they go about it:
"When we started work among the Lower Ramu language groups back in 2002 we were introduced to a new method for developing alphabets. This new method relied more on input from the speakers of the language and less on the linguistic expertise of the expat translator. Using this method, alphabets could be developed for many languages during the course of a two-week long Alphabet Design Workshop. Here is how it worked in the Marangis language group where we conducted an alphabet design workshop in 2003.
The first day of the workshop saw about a dozen men and women ready to work on an alphabet for their previously unwritten language. That morning we gave them the assignment that each of them would write a short story, using their knowledge of the english alphabet, in the Marangis language. If there were sounds that they did not know how to write they were just supposed to make up a temporary symbol, or leave a blank. We would work on finding a way to write it later. At first they were a bit intimidated by the idea but most of the participants soon got into the flow of the assignment.
Once the stories were completed, each writer read their story out loud to the group. When they had all read their stories the group selected one to put on the blackboard. The author carefully wrote his story on the board and then the fun began.
At the top of the blackboard we listed each letter that had been used in the story, in roughly the same order as the english alphabet. Then starting with the first letter on the list, we asked the participants to give us three words which start with that sound, three words with the sound in the middle, and three words ending in that sound. These words were listed on a second blackboard. This is actually harder than it sounds and it was often a bit of a struggle to find nine words for each sound. And some sounds simply do not occur in all positions in a word.
As we wrote out the words, occasionally a new sound would be found that had not occured in the original story. Those sounds would be added to the alphabet on the top of the blackboard. As the workshop went on the list of words and sounds grew until by the end of the third day we had covered all the sounds so the participants’ satisfaction. Now it was time to decide how to write those sounds.
Much of this was fairly straight forward. Since English is the national language of Papua New Guinea, we use the English alphabet as the basis for the alphabets we develop for the vernacular languages. And many of the sounds in the vernacular correspond nicely with the sounds in English. So, for example, we write the “s” sound as s and the “t” sound as t. But what about sounds that do not have a corresponding english sound?
In this case we try to find an letter in the English aphabet that is somewhat close to the sound in the vernacular. Or if there is simply no good correspondence we might use what we call a special character. A common special character in PNG languages is the barred i. This is an i with a cross through it and it represents a central vowel that does not exist in English.
There is often a lot of discussion as the participants work to decide how to write their language. Our role is to offer alternatives, show what other language groups have done with similar sounds, and help guide the discussion. Since it is their languages it is ultimately their decision how to write it."