code: private void appendSpellFields(I_CmsSearchDocument document) {
  
          /*
           * Add the content fields (multiple for contents with more than one locale)
           */
          // add the content_<locale> fields to this configuration
          String title = document.getFieldValueAsString(
              CmsPropertyDefinition.PROPERTY_TITLE + CmsSearchField.FIELD_DYNAMIC_PROPERTIES_DIRECT);
          document.addSearchField(
              new CmsSolrField(CmsSearchField.FIELD_SPELL, null, null, null),
              document.getFieldValueAsString(CmsSearchField.FIELD_CONTENT) + "\n" + title);
          for (Locale locale : OpenCms.getLocaleManager().getAvailableLocales()) {
              document.addSearchField(
                  new CmsSolrField(locale + "_" + CmsSearchField.FIELD_SPELL, null, locale, null),
                  document.getFieldValueAsString(
                      CmsSearchFieldConfiguration.getLocaleExtendedName(CmsSearchField.FIELD_CONTENT, locale))
                      + "\n"
                      + title);
          }
      }
docs: Copy the content and the title property of the document to a spell field / a language specific spell field.
  @param document the document that gets extended by the spell fields.