Hey there, welcome to the french community !
We are also struggling to find a correct method to get our own client french. I'm waiting to find a valuable source to make a official post here for new playes but for now, i can provide you the download link from a old french private server here. It's comming from this website. I havent install it cause i have the client in english for the same reason you want yours in french, but most of the player i have talk with told me it was okay.
Hope it will help you, and i will be more than gratefull if you give us a feedback or if you find another way to achieve your purpose.