code: public Map<String, Map<String, Set<String>>> getTargetLanguagesMap() {
          if (targetLanguagesMap == null) {
              assert false;
              return Collections.emptyMap();
          }
          return Collections.unmodifiableMap(targetLanguagesMap);
      }
docs: Returns the map containing target languages indexed by document type and ids.
  This method always returns non-null map.
  
  @return  The map containing target languages indexed by document type and ids.