Translating from one language into another is not an easy job. Translating from one language into another without losing some part of the meaning is an impossible job. There are few films and stories illustrating these difficulties. One of them, of course, is “Lost in translation“.
If you need another example, check these “lost in translation” web site. What goes on there is you can try any phrase you like to be translated by computer into few languages and then back to English. See if you notice any differences. :)