public   static  String replaceDoubleQuotas (String source)
    {
        StringBuffer dest =  new  StringBuffer();
         boolean  hasPair = false;
         char [] chars = source.toCharArray();
         for  ( int  i =  0 ; i < chars.length; i++) {
             char  ch = chars[i];
             if  (ch == '"') {
                 if  (hasPair) {
                    dest.append("& raquo;");
                }  else  {
                    dest.append("& laquo;");
                }
                hasPair = !hasPair;
            }  else  {
                dest.append(ch);
            }
        }

         return  dest.toString();
    }

with t as (select '"УАЗ" в народе считается "машиной" хорошей' as str from dual) 
select trim(regexp_replace(regexp_replace(' ' || t.str || ' ', '(" )', '&'||'raquo; '), '( ")',' &'||'laquo;')) from t

with t as (select '"УАЗ" в народе считается "машиной" хорошей' as str from dual) 
select trim(replace(replace(' ' || t.str || ' ', '" ', '&'||'raquo; '), ' "',' &'||'laquo;')) from t