Transliterate/transpose the characters in the NSString

If you don't need diacritics or accents you can call CFStringTransform(bufferRef, NULL, kCFStringTransformStripCombiningMarks, false);

Additional article: http://nshipster.com/cfstringtransform/

Either try CFStringTransform function of CFMutableString with kCFStringTransformToLatin transform identifier or make a NSString category with simple mapping.

Edited by the question poster: more specifically it should be:

NSMutableString *buffer = [@"русский язык" mutableCopy];
CFMutableStringRef bufferRef = (__bridge CFMutableStringRef)buffer;
CFStringTransform(bufferRef, NULL, kCFStringTransformToLatin, false);
NSLog(@"%@", buffer); // outputs "russkij âzyk"