add translation and french language


![frenchscreen](https://cloud.githubusercontent.com/assets/4963867/3012694/d358b392-df3c-11e3-9f4d-e0b8da007bb1.png)
![menu](https://cloud.githubusercontent.com/assets/4963867/3012699/df8b0192-df3c-11e3-8af0-0ae98b4de149.png)

all phrases need to be wrapped with the function _(). if the content has been translated, it's replaced with the new translation. if not, there is no changes. (So no need to create an english dictionnary)

i'v have written a doc to explain how to create or edit a language in /doc/translation.txt