nls: add native language support

- adds labwc.pot and po files for de, es, it and sv
- added notes in NEWS.md and CONTRIBUTING.md
- addresses #269
- conditional upon `msgfmt` being installed
- can be disabled at build time

po/de.po

@@ -0,0 +1,50 @@
+# Labwc pot file
+# Copyright (C) 2022
+# This file is distributed under the same license as the labwc package.
+# FIRST AUTHOR <https://github.com/Consolatis>, 2022.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: labwc\n"
+"Report-Msgid-Bugs-To: https://github.com/labwc/labwc/issues\n"
+"POT-Creation-Date: 2022-04-30 16:43+1000\n"
+"PO-Revision-Date: 2022-04-30 16:50+1000\n"
+"Last-Translator: Consolatis <https://github.com/Consolatis>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: German\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+
+#: src/menu/menu.c:428
+msgid "Reconfigure"
+msgstr "Rekonfigurieren"
+
+#: src/menu/menu.c:430
+msgid "Exit"
+msgstr "Beenden"
+
+#: src/menu/menu.c:446
+msgid "Minimize"
+msgstr "Minimieren"
+
+#: src/menu/menu.c:448
+msgid "Maximize"
+msgstr "Maximieren"
+
+#: src/menu/menu.c:450
+msgid "Fullscreen"
+msgstr "Vollbild"
+
+#: src/menu/menu.c:452
+msgid "Decorations"
+msgstr "Dekorationen"
+
+#: src/menu/menu.c:454
+msgid "AlwaysOnTop"
+msgstr "Immer im Vordergrund"
+
+#: src/menu/menu.c:456
+msgid "Close"
+msgstr "Schließen"