American born and raised in France but working in…

OK – it’s a complicated situation (especially for the French side of things) – but for US tax purposes, it probably doesn’t really matter which country he indicates for claiming the FEIE. And, since he appears not to have a residence address in Ireland, France might be the simpler option (for IRS purposes). Probably best to use the country that he is listing for his address for filing purposes (i.e. where he would receive any notifications from the IRS). But the IRS doesn’t really check out the details too carefully on these sorts of returns.