[billfruit]

I would reckon that even more than spelling, the subtleties of stressed and unstressed intonation of syllables in English is perhaps more difficult to grasp,for example most Indian speakers would find it almost impossible, as generally the Indian languages lack those (unless we consider prosody).

I personally feel stress is an ambiguous term for the concept, for English atleast it is more about the duration of a sound, rather than the intensity of it.