Ignore non-standard languages in Wikimedia OPML generator

xquery/opml/wikimedia.xqy

@@ -1,13 +1,16 @@
 declare function local:get-feeds($url as xs:anyURI, $language as xs:string) as node()* {
   doc(resolve-uri('./w/index.php?title=Special:SiteMatrix', $url))//link[@rel = 'alternate'][@type = 'application/rss+xml' or @type = 'application/atom+xml']
-  ! <outline
-    type="rss"
-    text="{@title}"
-    version="{if (@type = 'application/atom+xml') then 'ATOM' else 'RSS'}"
-    xmlUrl="{resolve-uri(@href, $url)}"
-    htmlUrl="{$url}"
-    language="{$language}"
-  />
+  ! element outline {
+    attribute type { "rss" },
+    attribute text { @title },
+    attribute version { if (@type = 'application/atom+xml') then 'ATOM' else 'RSS' },
+    attribute xmlUrl { resolve-uri(@href, $url) },
+    attribute htmlUrl { $url },
+    (: Some languages are not actual language codes, like `wikidata` or `labs` or `wikimania2008`, so we do not include them :)
+    if (fn:matches($language, "\d|^\w{4,}"))
+    then ()
+    else attribute { "language" } { $language }
+  }
 };
 
 doc('https://commons.wikimedia.org/w/api.php?action=sitematrix&amp;format=xml')//sitematrix