Will be any translated content (manually) counted by google and other search engines as unique? Ofcourse if there was no any such translation before.
It the translated text is unique, then it is unique. It will never be considered a duplicate or the original language text if that is what you are asking.
As google have translation service maybe it checks content at least on major languages for duplication?
Well, they can probably know if the page is about the same *subject*, but if it's in a different language, it's unique. For example, Google translates your post into spanish as: "¿Pero comparan realmente el contenido en diversas idiomas?" If you translate that back into English, using the same tool, it says: "But really compares the content in diverse languages?" So, the Spanish translation is OK, but back into English it sounds totally different, and with other languages (like German,French,etc) it would be even worse. Translation tools are not very good, so if you translate manually, no computer can tell that the content is duplicate (at least, not if you do a good job translating).
Hmm i use automatic translation offenly too, but always then correct the text. As i understand here minimal changes will create unique content?
Yes, minimal changes will create unique content, but if you want people to read and understand that content, I don't think it will work. Usually, translation tools are good enough for you to understand something, but visitors to a site will be turned off by the poor grammar, if they can understand it at all. If you are going to translate, translate manually.