docbook5 template: use lang and subtitle variables (#3855)

data/templates/default.docbook5

@@ -5,9 +5,15 @@
 $if(mathml)$
   xmlns:mml="http://www.w3.org/1998/Math/MathML"
 $endif$
-  xmlns:xlink="http://www.w3.org/1999/xlink" >
+  xmlns:xlink="http://www.w3.org/1999/xlink"
+$if(lang)$ 
+  xml:lang="$lang$"
+$endif$ >
   <info>
     <title>$title$</title>
+$if(subtitle)$
+    <subtitle>$subtitle$</subtitle>
+$endif$
 $if(author)$
     <authorgroup>
 $for(author)$

test/writer.docbook5

@@ -2,7 +2,8 @@
 <!DOCTYPE article>
 <article
   xmlns="http://docbook.org/ns/docbook" version="5.0"
-  xmlns:xlink="http://www.w3.org/1999/xlink" >
+  xmlns:xlink="http://www.w3.org/1999/xlink"
+ >
   <info>
     <title>Pandoc Test Suite</title>
     <authorgroup>