All monsters will respond with something when you talk to them, however not all will want to talk with you, and may just tell you 'I have nothing to say to you.'.

Some monsters such as Achman, the guild masters, the bank teller when you talk to them a menu will be displayed to help you with talking to them. Others may just tell you some information, and you should try 'talk to monster about information'. This format while somewhat long, is used instead of having the monster just watch what is said in the room. (The players decided on talk to monster about....).

If there is a monster that you feel should give more information when you typed talk to monster, please use the 'bug' command and explain in detail what you think needs to happen. This is a relatively new feature in monsters, and there may still be monsters that dont do enough when you talk to them.