Why is BOM required to use unicode in tokens?

[GK]

On Tuesday, 15 September 2020 at 16:23:01 UTC, Jon Degenhardt 
wrote:

> # The 'Ш' and 'ä' characters are fine.
> $ echo $'import std.stdio; void Шä() { writeln("Hello World!"); 
> } void main() { Шä(); }' | dmd -run -
> Hello World!
>
> # But not '∂'
> $ echo $'import std.stdio; void x∂() { writeln("Hello World!"); 
> } void main() { x∂(); }' | dmd -run -
> __stdin.d(1): Error: char 0x2202 not allowed in identifier

Yes. The same troubles for widely used Greek symbols (Sigma, 
alpha and some other). Unfortunally...