Okay so I found a solution (two to be exact) :
First solution: FB Graph API call /me?fields=location{location} will return :
"location": {
"location": {
"city": "Ottawa",
"country": "Canada",
"latitude": 45.4167,
"longitude": -75.7,
"state": "ON",
"zip": "<<not-applicable>>"
},
Then you just have to get result["location"]["location"]["country"]
Second solution is to get the user's locale if location is not defined, this will return something like :
fr_FR, the FR = the country code