Backport change from r115807 in Emacs trunk

doc/org.texi

@@ -16,6 +16,8 @@
 @set MAINTAINER Carsten Dominik
 @set MAINTAINEREMAIL @email{carsten at orgmode dot org}
 @set MAINTAINERCONTACT @uref{mailto:carsten at orgmode dot org,contact the maintainer}
+@documentencoding UTF-8
+@documentlanguage en
 @c %**end of header
 @finalout