NSArray *languages = [NSLocale preferredLanguages];
NSString *currentLanguage = [languages objectAtIndex:0];

preferredLanguages : (
zh-Hans,
en,
ja,
fr,
zh-Hant,
de,
nl,
it,
es,
pt-PT,
da,
fi,
nb,
sv,
ko,
ru,
pl,
pt,
tr,
uk
)