Do you mean that you want to be a nurse in a humanitarian setting?
I used to work for a humanitarian organisation (albeit not in any medical capacity) and you are right that you would greatly increase your chances of being employed if you spoke a second language, especially Arabic or French. However, the post-qualifying experience you have matters just as much, if not more - organisations like MSF tend to recruit healthcare staff with expertise in HIV/AIDS, tuberculosis, tropical medicine, or psychological trauma. So have a think about how you will get the relevant experience.
If you're serious about a career in this sector, then there are some reasonably priced intensive language courses over in France, of varying lengths. You could defer your nursing place for a year and sign up to one, if you can afford it, or you could find a tutor/take evening courses during your nursing degree and then save up money towards more intensive language training once you're working as a nurse.