You can try encoding IPTC metadata as Unicode(UTF-8), assuming Flickr supports it.
To do, select the "Write IPTC as Unicode" checkbox in Preferences-->IPTC/XMP, then select the OK button to save the changes.
You can also try deselecting the "Add embedded IPTC(XMP will always be written)" checkbox in the "For JPEG, TIFF, PSD, DNG photos" section to see if Flickr will read from XMP metadata, which is UTF-8.