I understood your confusion, but I guess you didn't understand my explanation.
It is really fairly simple. You give ExifTool a string of bytes and tell it
what character encoding was used. As long as ExifTool thinks that
the internal and external character sets are the same, then no translation
is performed and the bytes are passed through unchanged. (This is the
behaviour of older ExifTool versions for IPTC information.)
As long as ExifTool is not translating the text, it is totally irrelevant
what character set is actually used since the bytes are passed
through unchanged. So as long as ExifTool believes there is no need
to translate the text, you are free to use whatever character set you
I can see how this could be confusing.
If possible, it is best to use UTF8 to avoid this confusion.