Bonjour Emmanuel,
Hopefully you'll manage to find long-term accommodation during your time in Ireland! Apartment hunting can be tough if you aren't on the island already but I'm sure you'll end up finding something
While I don't have additional suggestions (rental platforms and ex-pats Facebook groups can already keep you busy), it might be easier to locate places to stay right outside of the main cities. You'll also find useful tips about long term stay and accommodation on the
French embassy in Ireland website.
If you don't intend to stay the whole time in one location, you might consider
WWOOFing, a system where you receive food and accommodation in exchange of work at organic farms.
Best of luck!
A bientôt,
Antoine