I'm not sure, but I think that you have to use Dart language to use Flutter.
Incidentally, I was pretty sure that Dart was dead. Turns out it's alive. I'm not sure what it is currently, now that it's statically typed, null safe and all. What are Dart's killer features?
It's not clear to me that killer features are really a thing for most languages. Sure Haskell has laziness/purity and Rust has ownership.
But what is C++'s "killer feature"? C interop? It used to be OOP but it's not that any more and yet C++ is still massively successful. What is Java's killer feature? GC? C#'s?
I think most languages don't have killer features, they have killer platforms and frameworks. For C, it was Unix. For Java, it was servers and the broad set of libraries. For C# it was WinForms and now Unity. For JS, obviously, the web.
Incidentally, I was pretty sure that Dart was dead. Turns out it's alive. I'm not sure what it is currently, now that it's statically typed, null safe and all. What are Dart's killer features?