Quite a big one actually, natural language processing is very difficult. It took until the past couple years to solve that one properly. There is a reason only humans have a complex language.

Having the same sound be spelled two different ways is a flaw of the writing system. The spoken word is always the real language in linguistic terms. If the writing system is hard to understand or to use then it’s a bad system. Hangul is much better from what I understand, as it always reflects the way something is pronounced.