impossible to get the donation form translated

I have a form for donation that I wanted to be displayed in french. I translated the english file to french, put it in the language fr-FR directory and despite this usual procedure nothing happens for the form elements related to the donor (first name, ...zip and so on).
More, I put my french translation file in the en-GB dir and changed its name to en-GB. Guess what ? nothing happens !
So what now ?
Tell me why this happens ! I never saw this with any component.
thanks

Hi,
You need to go to Backend -> Joom Donation -> Manage Custom Fields and open your existing custom extra fields and translate titles of fields
Thanks
Dam