Meson: Add 'nls' option to disable translation

It is not always needed to generate and install gmo files, for example
when building for Android or Windows that often doesn't have libintl to
use them anyway.

At least all GStreamer modules have this same option.

meson.build

@@ -1796,8 +1796,6 @@ glib_conf.set('HAVE_DCGETTEXT', 1)
 glib_conf.set('HAVE_GETTEXT', 1)
 
 glib_conf.set_quoted('GLIB_LOCALE_DIR', join_paths(glib_datadir, 'locale'))
-# xgettext is optional (on Windows for instance)
-xgettext = find_program('xgettext', required : false)
 
 # libmount is only used by gio, but we need to fetch the libs to generate the
 # pkg-config file below
@@ -1981,12 +1979,14 @@ subdir('gobject')
 subdir('gthread')
 subdir('gmodule')
 subdir('gio')
-if xgettext.found()
-  subdir('po')
-endif
 subdir('fuzzing')
 subdir('tests')
 
+# xgettext is optional (on Windows for instance)
+if find_program('xgettext', required : get_option('nls')).found()
+  subdir('po')
+endif
+
 # Install glib-gettextize executable, if a UNIX-style shell is found
 if have_sh
   # These should not contain " quotes around the values

meson_options.txt

@@ -83,3 +83,9 @@ option('installed_tests',
        type : 'boolean',
        value : false,
        description : 'enable installed tests')
+
+option('nls',
+       type : 'feature',
+       value : 'auto',
+       yield: true,
+       description : 'Enable native language support (translations)')