[Recurecur]

I'd take a long, hard look at Julia if I were you.

It has a lot in common with Nim, but is backed by a much larger community. Its FFI interface for C functions is faster than...C.

If Julia doesn't fit your use case(s), Rust might also be worth a look. What worries me about Rust is that it looks to me to have an awful lot of boilerplate that detracts from readability.