utils: Add missing file headers

utils/conv-lang.pl

@@ -1,5 +1,10 @@
 #!/usr/bin/env perl
 
+# This file is part of OpenTTD.
+# OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+# OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+
 use strict;
 use warnings;