code: public XPointerEngine setLanguage(final String language)
      {
          if (language == null)
          {
              this.languageValue = XdmEmptySequence.getInstance();
          }
          else
          {
              this.languageValue = new XdmAtomicValue(language);
          }
          return this;
      }
docs: Setting the language for the pointer resolution
  The language is used for xml:lang calculation
  
  @param language of the parent xml
  @return the XPointerEngine for fluent api usage