This is the 186th most frequent Indonesian word.
sekali
"Very" or "once."
In this sentence, 'sekali' is used as an intensifier to emphasize the degree of happiness, translating to 'very'.
Saya senang sekali hari ini.
I am very happy today.
Here, 'sekali' specifies frequency, meaning 'once'.
Dia datang sekali saja bulan ini.
He came only once this month.
In this context, 'sekali' acts as an intensifier, translating close to 'very'.