Problem with translations

Hello,

I am developing a 2-language site with Drupal and I have faced a problem. For example, I have a page About Us in 2 languages, however, when using language switcher, nothing happens with the text on the page, only link changes to another country code(eg en/ch). Last time I saw a module which adds Translate button, there I can assign the translated nodes to 1 node, so that the switching can be done right, however, I forgot the name of it...

Thanks in advance.