I could create QR codes of "日本語"(japanese) and "Márti" with following libraries:
You can read those QR codes with ZBar.
NSString* orginalString = @"Márti"(or "日本語"(japanese));
NSString *data = [[NSString alloc] initWithFormat:@"\357\273\277%@", orginalString];
UIImage* qrcodeImage = [QRCodeGenerator qrImageForString:data imageSize:imageView.bounds.size.width];
QR-Code-Encoder-for-Objective-C:
NSString* orginalString = @"Márti"(or "日本語"(japanese));
NSString *data = [[NSString alloc] initWithFormat:@"\357\273\277%@", orginalString];
//first encode the string into a matrix of bools, TRUE for black dot and FALSE for white. Let the encoder decide the error correction level and version
DataMatrix* qrMatrix = [QREncoder encodeWithECLevel:QR_ECLEVEL_AUTO version:QR_VERSION_AUTO string:data];
//then render the matrix
UIImage* qrcodeImage = [QREncoder renderDataMatrix:qrMatrix imageDimension:qrcodeImageDimension];