Japanese. Well, not all whitespace is irrelevant, but words in sentences are not required to be separated by spaces. In the kanji writing system, a word's function in the sentence is indicated by a particle (a very small word which proceeds it). Particles indicate objects and subjects of the sentence, as well as many notions that are expressed in English through prepositional phrases. When kanji is written horizontally as western languages are, periods and spaces are used as in English to denote the end of sentences. However (although I'm not entirely sure about this), no periods or spacing are required when using the antiquated, stylistic vertical method of writing kanji.