「不一定」的英文點寫?

not necessarily

Is uncertain

"Not necessarily"

not really, may be, perhaps, could be, not necessary, depends, etc

There are a lots of ways to write it. It really depends on where you want to apply the words.

we cannot directly translate 「不一定」and use it like chinese
usually we say:

it depends

maybe,,

Maybe ; perhaps ; probably
either ; or ; uncertain; not sure; not necessarily so; contingent

Not certainly.