configure.in has

XDT_I18N([ar ast be bg ca cs da de el en_GB es eu fr gl hu id it ja kk lv pl pt_BR pt ro ru sk <-- HERE

but no file po/sk.po in release tarball, causing:

export LINGUAS="sk"
./configure
make
make install

fails with:

Making all in po
make[2]: Entering directory `/tmp/portage/xfce-extra/xfce4-xkb-plugin-0.5.4.1/work/xfce4-xkb-plugin-0.5.4.1/po'
file=`echo ca | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file ca.po
file=`echo cs | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file cs.po
file=`echo da | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file da.po
file=`echo de | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file de.po
file=`echo el | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file el.po
file=`echo es | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file es.po
file=`echo fr | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file fr.po
file=`echo gl | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file gl.po
file=`echo hu | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file hu.po
file=`echo it | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file it.po
file=`echo pl | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file pl.po
file=`echo pt | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file pt.po
file=`echo ro | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file ro.po
file=`echo ru | sed 's,.*/,,'`.gmo \
  && rm -f $file && /usr/bin/gmsgfmt -o $file ru.po
make[2]: *** No rule to make target `sk.gmo', needed by `all-yes'.  Stop.
make[2]: *** Waiting for unfinished jobs....
make[2]: Leaving directory `/tmp/portage/xfce-extra/xfce4-xkb-plugin-0.5.4.1/work/xfce4-xkb-plugin-0.5.4.1/po'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/tmp/portage/xfce-extra/xfce4-xkb-plugin-0.5.4.1/work/xfce4-xkb-plugin-0.5.4.1'
make: *** [all] Error 2

this is because git shouldn't have file LINGUAS in po/ directory anymore, and the package needs to be updated to latest xfce4-dev-tools or otherwise all release tarballs will end up broken