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

src/main.c

@@ -32,6 +32,11 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
+#if HAVE_NLS
+	setlocale(LC_ALL, "");
+	bindtextdomain(GETTEXT_PACKAGE, LOCALEDIR);
+	textdomain(GETTEXT_PACKAGE);
+#endif
 	char *startup_cmd = NULL;
 	char *config_file = NULL;
 	enum wlr_log_importance verbosity = WLR_ERROR;