This is due to unicode and more about how the special character is displayed. Unicode characters will display differently in Notepad and Wordpad for example.
In your case, it appears this special character is confusing the XCopy command and making it think it is a file, and not a folder.
If it is an option, change it to an e and then try it again. I appreciate it's not ideal as you're having to create a new word but this should work. If it does, then you know the issue is with the character, if not then obviously you'll need to investigate further.
I can't test this, but you could try Robocopy (not sure what OS you're using)
robocopy" C:\Users\Administrator\věc" "C:\věc"
Or, the issue is, your machine is not showing you file extensions, so you think your file is
věc . It is not likely! Your file should be name dot extensions
věc.txt or věc.pdf