Migrate from intltool to gettext translation

Quoting fragments from one of the commit messages:

[0] GNOME Goal: Gettext Migration

This goal from 2016 is to migrate away from using intltool to help
translate epsecially GNOME application related files, and instead use
gettext directly now that gettext can handle a lot more file formats
[1][2][3].

The GNOME Goal: Gettext Migration [0] says:

"With gettext 0.19.8, there is really no need anymore to use
intltool or GLib’s dated gettext glue (AM_GLIB_GNU_GETTEXT and
glib-gettextize)."

...

Additionally the use of intltool and the associated GLib provided macro AM_GLIB_GNU_GETTEXT was the source of the remaining warnings from autoconf 2.71 seen in Fedora 36 and Ubuntu 22.04 LTS about the use of obsolete macros:

$ ./autogen.sh  
...  
autoreconf: running: /usr/bin/autoconf --force  
configure.ac:59: warning: The macro `GLIB_GNU_GETTEXT' is obsolete.  
configure.ac:59: You should run autoupdate.  
aclocal.m4:426: GLIB_GNU_GETTEXT is expanded from...  
aclocal.m4:526: AM_GLIB_GNU_GETTEXT is expanded from...  
configure.ac:59: the top level  
configure.ac:59: warning: The macro `AC_TRY_LINK' is obsolete.  
configure.ac:59: You should run autoupdate.  
./lib/autoconf/general.m4:2920: AC_TRY_LINK is expanded from...  
lib/m4sugar/m4sh.m4:692: _AS_IF_ELSE is expanded from...  
lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...  
./lib/autoconf/general.m4:2249: AC_CACHE_VAL is expanded from...  
./lib/autoconf/general.m4:2270: AC_CACHE_CHECK is expanded from...  
aclocal.m4:111: GLIB_LC_MESSAGES is expanded from...  
aclocal.m4:426: GLIB_GNU_GETTEXT is expanded from...  
aclocal.m4:526: AM_GLIB_GNU_GETTEXT is expanded from...  
configure.ac:59: the top level  
configure.ac:59: warning: The macro `AC_TRY_LINK' is obsolete.  
configure.ac:59: You should run autoupdate.

...

[1] Migrating from Intltool to Gettext
[2] Using Modern Gettext
[3] On the killing of intltool