Manually check for xgettext as we need it for NLS support.
Review Request #548 — Created Feb. 28, 2021 and submitted
See https://github.com/mesonbuild/meson/issues/8436 for the upstream bug this is working around.
Also fixed an issue where the appdata file was causing configuration to fail if nls was turned off.
Ran locally with
-Dnls=trueand-Dnls=false.
