code: public static boolean isLetter(String str, int beginIndex, int endIndex)
      {
          for ( int i = beginIndex; i < endIndex; i++ ) {
              char chr = str.charAt(i);
              if ( ! StringUtil.isEnLetter(chr) ) {
                  return false;
              }
          }
  
          return true;
      }
docs: check if the specified string is Latin letter
  
  @param   str
  @param   beginIndex
  @param   endIndex
  @return  boolean