Indonesian uses the same twenty-six letters as English. There is no new script to learn, no accents, no characters that do not exist on your keyboard. For a language this far from Europe, that is unusual and it is a large part of why Indonesian is quick to start.
What differs is how the letters are named, and you need that the first time someone asks you to spell your name over the phone.
The letter names
a, bé, cé, dé, é, éf, gé, ha, i, jé, ka, él, ém, én, o, pé, ki, ér, és, té, u, vé, wé, éks, yé, zét
Most follow the Dutch and Latin pattern rather than the English one. The ones that catch English speakers:
c is cé, not “see”
g is gé, not “jee”
j is jé, not “jay”
q is ki
y is yé
z is zét
Spelling something out
Bagaimana dieja? ‘How is it spelled?’
L, O, I, C. Said as él, o, i, cé.
Expect to do this often. Foreign names are unfamiliar here, and being able to spell yours slowly is worth more than it sounds.
The four two-letter sounds
kh, ng, ny and sy each represent one sound, not two. They get their own lesson, but note now that they are treated as single units when spelling: ng is said èn-gé.
Why you see Soekarno and Sukarno
Indonesian changed its spelling in 1972, replacing the Dutch conventions inherited from colonial rule.
oe became u
tj became c
dj became j
j became y
So Soekarno became Sukarno, and Djakarta became Jakarta. Both spellings survive, because people kept the old form in their own names: you will meet Indonesians spelling themselves Soetomo and Widjaja today.
This matters practically. When you see oe in a name, read it as u. When you see dj, read it as j. Otherwise you will pronounce half the street names in Jakarta wrong.