[pouetpouet]

The alphabet is a phenomenal invention. I mean the alphabet in the large sense, be it the Latin, Greek, Russian alphabet or any alphabet, abjad, abudiga or syllabary. The Chinese writing system is a notable exception (along with Japanese Kanji and some others). The only complicated thing about Chinese is pronunciation and writing system. So half of it is complicated. If a language can be characterized at least by phonology, writing system, grammar and vocabulary. Then Chinese is difficult. Not that any language is easy. There will never be an agreement for the whole world to speak Chinese.

[sametmax]

The alphabet, and punctuation.

Omitting punctuation, or using some meta language for it (e.g: in thai, repeatiting a word can mean "!") makes reading some text extra difficult.