I would like to use Umbraco CMS. But I need to know is there availible changing admin User Interface language to Polish? So that the whole admin stuff and everything would be in Polish language.
I don't need Multi-Language functionality.
I know that there are availible other language packs (like German), so is there also Polish language pack?
Yes, Polish is available out of the box in the umbraco backoffice. I don't know what the quality of the translation is though, so you'll have to have a look at that yourself.