Be careful here.
As far as I recall, the tax treaty between Ireland and France was signed back in the late 1960's.
Capital Gains Tax was introduced in Ireland in the mid 1970's.
Therefore, the tax treaty might not cover Capital Gains Tax in Ireland and you might not be allowed a credit in Ireland for the tax paid in France. One of the Ryan family (of Ryanair fame) took a case to the Supreme Court a few years ago on this matter related to the Ireland-Italy treaty, which also pre-dates the introduction of CGT to Ireland, but the result might not be applicable here (different terms in this treaty)
I would definitely consult a tax advisor in Ireland to be certain before filing your Irish capital gains tax return. At the very least, I would "express a doubt" in the return if you're claiming the credit so that you're protected from interest and penalties.