diff --git a/language.php b/language.php
index 8e1423b..87dff78 100644
--- a/language.php
+++ b/language.php
@@ -340,4 +340,12 @@ class language
         throw new Exception ("No language available for '$languageCode'", 500);
     }
   }
+
+  /** Return the language subtag for the language
+      http://www.iana.org/assignments/language-subtag-registry/
+      language-subtag-registry*/
+  public function languageSubTag ($languageCode)
+  {
+    return str_replace ("_", "-", $languageCode);
+  }
 }