[R] [Sweave] doesn't accept unicode?

[moonkid at posteo.org]

Of course I manage and write my tex-files in unicode (utf-8) (running 
XeTeX). That is why my R-output need to be in unicode, too.

But Sweave doesn't accept unicode files.

[R]
> Sweave("analy.Snw")
Fehler: ‘analy.Snw’ is not ASCII and does not declare an encoding
[/R]

[analy.Snw]
<<>>=
x <- ü

table(x)
@
[/analy.Snw]

How should I "declare an encoding". I can not find an option for the 
<<>>.

I don't have to declare any of my tex-files explicite because XeTeX use 
the files like they come. It knows for itself the encoding.