GNU gettext installs macros for use in a package’s
configure.ac or configure.in.
See Introduction in The Autoconf Manual.
In order to copy these macros into your package,
use the gettextize or autopoint programs.
See Invoking the gettextize Program or Invoking the autopoint Program.
Attempts to use the autoreconf program for this purpose are unreliable.
The primary macro is, of course, AM_GNU_GETTEXT.