As a french dev guy, all I can say is ... it depends, and you will need to have this conversation with your customer. Manual and user interface will probably ha

As a french dev guy, all I can say is ... it depends, and you will need to have this conversation with your customer. Manual and user interface will probably have to be in french. Regarding the code, you will probably be able to code/comment in whatever language you want, but ... some customer can be picky for whatever reason (internal IT guy/expert does not speak English, there is a current french power move against english at the european commission, etc..)