Thanks,
When you say not writing legacy IPTC, does that mean I should tick the "write IPTC as unicode" case?
Also, right now the Default IPTC encoding is Mac Roman, is that ok for French accents. I'm sorry I really don't know much about this tech stuff.
I was uploading to flicr when I noticed the problem, it also happened in Capture One when I used embeded metadatsa in RAW files, the issue doesn't exist since I moved to sidecar XMP.