I started out asking a question and then figured it out so thought I'd post what I found.
Using Lightroom 1 on a Mac, I entered keywords with a "LATIN SMALL LETTER E WITH ACUTE". exiftool was changing this to "LATIN CAPITAL LETTER Z WITH CARON". I was having trouble getting the -charset with the equals to work for me.
I was on Image-ExifTool-7.377 and upgraded to Image-ExifTool-8.18.
Anyhow, short story long, Lightroom 1 on a Mac stores the keywords encoded as macroman. Thus, this solved my problem:
exiftool -charset iptc=macroman -Keywords VC5Y0634.jpg
This same command with 7.377 prints: File not found: iptc=macroman
I tried surrounding it with quotes and that did not work either. In that case, I get: Sorry, charset is not writable
As a side note, there is no IPTC:CodedCharacterSet in the image and there is no way I can see to set it inside Lightroom.
Yes, the -charset option is a relatively recent addition.
I know if no utilities which except exiftool which allow writing the IPTC:CodedCharacterSet directly. Some of them will set it automatically, and many of them will ignore it altogether.
- Phil