use preferred language for config file retrieval

src/lib/ebus/filereader.h

@@ -222,6 +222,11 @@ class MappedFileReader : public FileReader {
    */
   static const string normalizeLanguage(const string& lang);
 
+  /**
+   * @return the preferred language code (up to 2 characters), or empty.
+   */
+  const string getPreferLanguage() const { return m_preferLanguage; }
+
   // @copydoc
   result_t readFromStream(istream* stream, const string& filename, const time_t& mtime, bool verbose,
       map<string, string>* defaults, string* errorDescription, bool replace = false, size_t* hash = nullptr,

src/lib/ebus/message.h

@@ -1267,7 +1267,7 @@ class MessageMap : public MappedFileReader {
    * @param deleteData whether to delete the scan message @a DataField during @a Message destruction.
    */
   explicit MessageMap(bool addAll = false, const string& preferLanguage = "", bool deleteData = true)
-  : MappedFileReader::MappedFileReader(true),
+  : MappedFileReader::MappedFileReader(true, preferLanguage),
     m_addAll(addAll), m_additionalScanMessages(false), m_maxIdLength(0), m_maxBroadcastIdLength(0),
     m_messageCount(0), m_conditionalMessageCount(0), m_passiveMessageCount(0) {
     m_scanMessage = Message::createScanMessage(false, deleteData);