Did you self-publish or was your book published by a publishing house in France?
Operating under the assumption that you self-published: I've seen different numbers for how well self-published books sell on average. Is there any way to figure out what the average sales numbers for books in French are? Then you can compare your numbers to those and see if they're close. If they compare well, you can mention it and say that your book sold well in your particular market.
I think even if you don't mention your sales, an interested agent would likely still ask you for the numbers before they even consider signing you.
(A fair warning: Generally, agents are reluctant to sign on projects that have been published before, although this might be different in this case since the book has been published in a different language.)
