Why literal translations don't work

"You Are My Sunshine" translated into Portugese, and back into English:

You it is my light of the sun, mine only light of the sun.
You it makes me happy when the skies are cinereous.
You'll never knows expensive how much I love you.
Please taken of don't my light of the moved away sun.


I recommend highly trying this with your favorite song (but do it one verse at a time otherwise, it's tooooo long) to and from any language of your choice.