I never had that word before in the course, it was not properly introduced.
It is arabic used by the arabic indonesians.
Does the "wa" infront mean "too"? Can we use it for any word then?
It´s arabic and not directly related to indonesian. It means something like the translation "greetings to you, too". In fact. the arabic version are multiple words and they mean "And peace/health/greetings/wellbeing on you"
The problem is: not everyone familiar with this greetings since this is not in Bahasa Indonesia.
Why Silakan not Tolong?
Because of the context. In this case, "please" is not understood as a mean to ask for a help. Instead, to allow and to greet someone.
the app rejects the correct Bahasa form - salam juga untukmu
salam juga untukmu is the correct from not what is given in Arabic
Can duolingo just use another greetings than this coz its not all indonesian use it and i think its not bahasa indonesia