When converting ANSI to Unicode, we use the system code page. So if you set the machine locale to Russian, we'll treat ANSI characters 128-255 as Russian.
We do not perform heuristics to guess how to map characters 128-255 (so we'd guess Russian even if you're using English as the system setting).
In my opinion, there's almost no reason for ANSI to exist in a stored file. UTF-8 or UTF-16 should be used for any text that contains characters over 127.