-IPTC:CodedCharacterSet=UTF8 (not UTF-8) works again as of version 6.86 (somehow this feature got broken before this version).

IPTC uses the ISO 2022 standard for alternate character sets, and character sets are specified via a sequence of escape characters. For UTF-8, the escape sequence is "ESC % G", and for convenience ExifTool allows you to also specify "UTF8" which is translated to the appropriate escape sequence internally.

You can use the -n option to bypass this translation to see actual escape sequence (but in this case, the "ESC" character will appear as a "." because all control characers are converted to "." in the output. But you can add the -b option to prevent this conversion too if you want.)

I hope this makes sense.

- Phil