From a basic search it appears that D can generate dynamically linked libraries (DLL , SO, etc) which will be the easiest way to extend pharo using D.

However from a very basic search I did it looks like generating dynamically linked libraries with D is not as straightforward as someone would expect.

http://forum.dlang.org/thread/k3vfm9$1tq$1@digitalmars.com

If you are not bound to D for creating system-level extensions for Pharo you have several options

1) nim language is used by gokr and his company and they use it to extend Squeak

here is a blog post about what nim is

http://hookrace.net/blog/what-is-special-about-nim/

and here is a blog post of gokr about how to get it to work with squeak and pharo

http://goran.krampe.se/2014/11/03/squeak-to-nim/

2) Maybe just maybe you could use Slang , which is basically smalltalk that compiles to C and is what the pharo VM uses a lot. But I am not certain.

PS: Just realised you commented on that blog post so you may be aware of all this, but you can take this as a friendly reminder of your potential solutions :)