Last updated on April 3, 2022
You should note that when the kinship term bapak (a father) used as second person pronouns (i.e. meaning “you”), Bapak is written with the initial capital B. But when it is used in their ordinary, referential sense as kinship terms it is not capitalised. Except at the beginning of a sentence, of course. The same thing with the kinship term ibu (a mother) used as second person pronouns (i.e. meaning “you”)
Bapak is the Javanese word for “a father” and ayah is the more traditionally Malay word. So you are more likely to hear ayah used in Sumatra and among educated speakers or “purists”. On the other hand, bapak has been enthusiastically adopted into Indonesian. You will commonly hear it used to refer to “a father”. Especially in Java and among less fastidious users of the language.
Ayah is used to mean “you” only when you are addressing your own real father. If you are not talking to your real father, but to a “pseudo-father” you should address him as Bapak with the initial capital B.