The fact that the Report is silent about encoding used to
a certain level of non-portability (and confusion.) I found
Specifying the encoding can *also* limit portability, if you specify an encoding that is not widely supported on some target platform. (Please try to remember that the universe is not composed solely of Windows and Linux. The fact that those are the only ones you care about is not relevant to the standard; nor is the list of platforms that GHC or any other implementation supports.)
Encoding does not belong in the language standard; it is an aspect of implementing the language standard on a given platform.