Chicken can't understand what ducks say, so 鸡同鸭讲 just means that someone has chosen the wrong audience or someone waste good acts on others who won't understand.
一目了然 just by taking a glance and then you get it.
Tom: 你知道中国是区域自治吗？ (You know that China has instituted a system of regional autonomy in minority areas.)
Anna: 真的假的？我一直以为中国是联邦制，跟美国一样... （what？ I was always thinking China got a federal system, just like the United States）
Tom: 哎，算了，我在这简直是鸡同鸭讲，中国怎么可能是联邦制啊...你不会连这都不懂吧？ （Never mind, when it comes to politik and law, we couldn't communicate xDxD. How could China even be federalism, so you really don't know that do you?）
Anna：你才是鸭子呢！中国虽然不是联邦制，不过也快了...(Oh, come on, you are the person who can' figure out the trend, china is still not ferdalism, but it will be soon...)
Tom: 这种趋势怎么可能一目了然， 你不会做白日梦梦见的吧,你不知道联邦制都是独立选举吗？... (How can I just by taking at a glance get to this conclusion that China will one day be ferdalism, so you must be daydreaming...Don't you see that all the staates who has ferdalism has it's seperated election system?)