* @return an OptionalEntity containing the dictionary file if found, empty otherwise
     */
    public OptionalEntity<DictionaryFile<? extends DictionaryItem>> getDictionaryFile(final String id) {
        for (final DictionaryFile<? extends DictionaryItem> dictFile : getDictionaryFiles()) {
            if (dictFile.getId().equals(id)) {
                return OptionalEntity.of(dictFile);