string(PAnsiChar(message)). This seems to do the job. The error messages will always be in English anyway.
I also discovered today that my "is it UTF-8?" detection code gives a false positive on GB18030 files (PRC Chinese encoding). This is annoying, but there's not much I can do about it. It just means that when opening such files in Transformer, it always suggests UTF-8 instead of GB18030.
Since I now have robust text file encoding conversion available, I think it would make sense to make this a batchable feature. I'll need to think about how best to do that, but it could be a part of the main batch screen, where you could specify the input encoding. There should be a new, initial tab entitled "Loading files", which should have a drop-down where you can specify the input encoding. You could discover this using the normal file-loading capabilities in the Source tab.