[OT] _("STRING") notation

[Sven Burgener <svenb@bluewin.ch>]

(This applies to programming in C)

What is the significance of the '_' character in the following usage?

        printf(_("This is fetchmail release %s"), VERSION);

Why the '_' and why the additional ()'s around the string constant?

This looks like _ does something special to the ()-part...?

Could the following have done the job just as well instead?

        printf("This is fetchmail release %s", VERSION);

Thanks for any insight