It appears that the string is partially escaped. If you encode "valószínű" into an NSData object using:
NSData * data = [@"valószínű" dataUsingEncoding:NSUTF8StringEncoding];
then created an attributed string using
NSAttributedString * attrString = [[NSAttributedString alloc] initWithHTML:data documentAttributes:nil];
the "u" will be properly converted, but the preceding marks would be mangled:
resulting in
valószÃnű
An alternative would be to see the following post: