What is "Iya"?
"Iya" = "ya"
We Indonesians looooove to shorten words. Example:
Terima kasih -> Makasih (thank you)
Tidak -> ga /gak (no)
Bagaimana -> gimana (how)
WE EVEN SHORTEN NAMES LMAO and called it nicknames
Well, to shorten names is usual in many languages/countries.
What are the various ways of saying yes, do they have different meanings and times of usage?
"iya" dan "ya" are the most common words to say yes in Indonesian. It can be used in every situation.
What is aissalamalaikum?
it's a greeting for Muslim. It means peace be upon you. Since most Indonesian peoples are muslim, so it like to be a normal greetings here.
It's arabic, not bahasa. It means : peace be upon you.