I am writing to let you know that I am interested in your offer.
I speak both English and French very well, I am experienced and devoted and until now I have worked on several translating projects at work. I have to say that all the people I have helped in real life with translation have been very content and now have trust in my writing skills and my ability to translate and understand any kind of documents.
I will also need more information about this job and I am looking forward to hearing from you as soon as possible, so we can talk about the project.