unicode.m

    NSString *s = @"L'asso du jour est g\\U00e9niale";
    
    NSMutableString *result = [NSMutableString string];
    NSScanner *scanner = [NSScanner scannerWithString:s];
    [scanner setCharactersToBeSkipped:nil];

    while (![scanner isAtEnd]) {
        NSString *chunk;

        [scanner scanUpToString:@"\\U" intoString:&chunk];
        [result appendString:chunk];
        
        if ([scanner scanString:@"\\U" intoString:nil]) {
            
            NSUInteger value = 0;
            NSRange range = NSMakeRange([scanner scanLocation], 4);
            NSString *code = [s substringWithRange:range];
            [[NSScanner scannerWithString:code] scanHexInt:&value];

            [result appendFormat:@"%C", (unichar)value];
            [scanner scanString:code intoString:nil];
        }
    }

    label.text = result;