diff -r c5b3860d29ef -r b6dacf6eabe3 src/Pure/Tools/spell_checker.scala
--- a/src/Pure/Tools/spell_checker.scala	Wed Nov 28 15:38:18 2018 +0100
+++ b/src/Pure/Tools/spell_checker.scala	Wed Nov 28 16:14:31 2018 +0100
@@ -66,7 +66,7 @@
 
   class Dictionary private[Spell_Checker](val path: Path)
   {
-    val lang = path.split_ext._1.base_name
+    val lang = path.split_ext._1.file_name
     val user_path = Path.explode("$ISABELLE_HOME_USER/dictionaries") + Path.basic(lang)
     override def toString: String = lang
   }