Typically: Russian / German
The reality: Imagine how Germans & Russians learnt it themselves ? Because they born with it & people spelled it over & over around their ear. Human own high powers & ability. Just think about the moment that all the languages been invented. Human brain is so powerful,strong, & flexible. Humans can learn anything they want, (apart from basic talents & two side of brain ect . .) if humans don't get lazy themselves, build their confident, stand under the pressure of learning, don't give up & continue forward. Practice properly. They'll eventually learn it. Anything that they want. So no language is hard to learn, it only comes hard when we don't wanna be strong enough to challenge ourselves.