diff --git a/src/main/resources/lang/lang.xml b/src/main/resources/lang/lang.xml
index 779cdd4d0..68f359c3c 100644
--- a/src/main/resources/lang/lang.xml
+++ b/src/main/resources/lang/lang.xml
@@ -2,16 +2,21 @@
 <!--
 To add a new language, you can add the language to this file.
 Use the name of the language in that language.
-Then copy the English language file "lang_en.xml", rename
-it and translate it into the new language.
+Then make a copy of the English language file "lang_en.xml"
+and rename it to "lang_xx_ref.xml". Then create a second
+copy and rename it to "lang_xx.xml". Then translate the
+latter file into the new language.
+
+The file "lang_xx_ref.xml" helps me to keep track of future
+changes to the language files.
 
 If you also want to translate the static part of the documentation,
 you have to translate one of the files "static_xx.xml" from the
 folder "src/test/Resources/Docu".
 
 If you are satisfied with the translation, please send me the
-translated version AND the file "lang_en.xml" you used for the
-translation! Both files are required to keep track of changes.
+translated version AND the file "lang_xx_ref.xml" you used for the
+translation!
 -->
 <languages>
     <lang name="en">English</lang>
diff --git a/src/test/java/de/neemann/digital/lang/TestLang.java b/src/test/java/de/neemann/digital/lang/TestLang.java
index 55f2780f0..a9a27ddd9 100644
--- a/src/test/java/de/neemann/digital/lang/TestLang.java
+++ b/src/test/java/de/neemann/digital/lang/TestLang.java
@@ -15,6 +15,7 @@ import java.io.*;
 import java.util.*;
 
 /**
+ * Checks the language files to make sure they a consistent.
  */
 public class TestLang extends TestCase {
     private static final String SOURCEPATH = "/home/hneemann/Dokumente/Java/digital/src/main/java";
@@ -42,7 +43,7 @@ public class TestLang extends TestCase {
     }
 
     /**
-     * Finds usages of keys which are not present in the language xml files
+     * Finds usages of keys in the code which are not present in the language xml files
      *
      * @throws IOException IOException
      */
@@ -70,6 +71,10 @@ public class TestLang extends TestCase {
             fail("there are unused language keys: " + sb.toString());
     }
 
+    /**
+     * Outputs all missing or modified language keys in languages which are not
+     * forced to be complete. (all languages except de and en)
+     */
     public void testAdditionalLanguages() {
         de.neemann.gui.language.Resources master = bundle.getResources("en");
         for (Language l : bundle.getSupportedLanguages()) {