when I should use "kali" & "sekali"?
Kali have different meaning depends on the sentence :
Kali : "river" (noun)
ex : 'Tidak jauh dari rumah kakek ada sebuah kali' > "Not far from grandfather's house there is a river"
Kali : "time"
ex : 'pertama kali belajar bahasa Indonesia' > "First time learning Indonesian"
'lain kali saat kita berjumpa, saya yang traktir Anda' > "Next time we meet, I treat you"
kali : "maybe" (slang word)
ex : 'Dia lagi di jalan kali' > "He is on the way maybe"
Sekali = satu kali = "once"/"one time"
ex : 'Saya pernah ke Indonesia sekali' > "I have been to Indonesia once"
Sekali and Kali can also have same meaning.
Sekali/Kali : "very"
sekali : formal ; kali : informal/slang
ex : 'Jalan ini panjang sekali' > "This road is very long"
'Jalan ini panjang kali' > "This road is vary long"